1. A digital watermarking based method for objectively evaluating quality of stereo image, comprising following steps of: {circle around (1)}-1 at a transmitting terminal, denoting an original undistorted stereo image as S org , denoting a left-view image of S org as L org and a right-view image of S org as R org ; dividing L org and R org respectively into M × N 8 × 8 image blocks which are non-overlapped with each other and have a size of 8×8, wherein M is a width of L org or R org , N is a height of L org or R org ; {circle around (1)}-2 processing discrete cosine transform (DCT) on each image block in L org and R org , so as to obtain a DCT coefficient matrix of each image block in L org and R org ; {circle around (1)}-3 processing coefficient reorganization on all DTC coefficients in the DCT coefficient matrix of all of the image blocks in L org and R org , so as to obtain 10 coefficient reorganized matrixes which are different from each other and respectively corresponding to L org and R org , denoting an n′th coefficient reorganized matrix corresponding to L org as S L,org n′ , denoting an n′th coefficient reorganized matrix corresponding to R org as S R,org n′ , wherein DCT coefficients having a same coordinate position in the DCT coefficient matrixes of all the image blocks in L org are located in a same coefficient reorganized matrix, and DCT coefficients having a same coordinate position in the DCT coefficient matrixes of all the image blocks in R org are located in a same coefficient reorganized matrix, wherein 1≦n′≦10; {circle around (1)}-4 calculating an absolute value matrix of a difference value of each coefficient reorganized matrix corresponding to L org and each coefficient reorganized matrix corresponding to R org , denoting an absolute value matrix of a difference value of an n′ th coefficient reorganized matrix S L,org n′ corresponding to L org and an n′ th coefficient reorganized matrix S R,org n′ corresponding to R org as D org n′ , denoting an l th coefficient of D org n′ as D org n′ (l), wherein D org n′ (l)=|S L,org n′ (l)−S R,org n′ (l)|; calculating an average value and a standard deviation of the absolute value matrix of the difference value of each coefficient reorganized matrix corresponding to L org and each coefficient reorganized matrix corresponding to R org , respectively denoting the average value and the standard deviation of D org n′ as μ r n′ and σ r n′ , wherein μ r n ′ = 1 L n ′ ∑ l = 1 L n ′ D org n ′ ( l ) , σ r n ′ = 1 L n ′ - 1 ∑ l = 1 L n ′ ( D org n ′ ( l ) - μ r n ′ ) 2 ; wherein S L,org n′ (l) represents an l th DCT coefficient in S L,org n′ , S R,org n′ (l) represents an l th DCT coefficient in S R,org n′ , wherein “∥” is an absolute value sign, 1≦l≦L n′ , wherein L n′ represents a total number of DCT coefficients in S L,org n′ or S R,org n′ ; {circle around (1)}-5 respectively processing filtering on all of the DCT coefficients in the DCT coefficient matrix of each image block in L org and R org utilizing Watson sensitivity operator, so as to obtain a filtered DCT coefficient matrix of each image block in L org and R org ; {circle around (1)}-6 respectively processing coefficient reorganization on the DCT coefficients of the filtered DCT coefficient matrix of all the image blocks in L org and R org utilizing the same way of coefficient reorganization as thereof in the step {circle around (1)}-3, so as to obtain 10 filtered coefficient reorganized matrixes which are respectively corresponding to L org and R org , and different from each other, denoting an n′th filtered coefficient reorganized matrix corresponding to L org as S L,org n′ , denoting an n′th filtered coefficient reorganized matrix corresponding to R org as S R,org n′ , wherein filtered DCT coefficients having a same coordinate position in the filtered DCT coefficient matrixes of all the image blocks in L org are located in a same filtered coefficient reorganized matrix, and filtered DCT coefficients having a same coordinate position in the filtered DCT coefficient matrixes of all the image blocks in R org are located in a same filtered coefficient reorganized matrix, wherein 1≦n≦10; {circle around (1)}-7 according to all of the filtered DCT coefficients in the 10 filtered coefficient reorganized matrixes respectively corresponding to L org and R org , calculating a first sensitivity threshold, which is denoted as T1, wherein T 1 = α × ∑ k = 1 10 ∑ l = 1 L k  S org _ k ( l )  / ∑ k = 1 10 L k , wherein α is a sensitivity threshold regulatory factor, 1≦k≦10, 1≦l≦L k , wherein L k represents a total number of filtered DCT coefficients of a k th filtered coefficient reorganized matrix in the 10 filtered coefficient reorganized matrixes respectively corresponding to L org or R org , wherein S org k (l) represents an l th filtered DCT coefficient of a k th filtered coefficient reorganized matrix in the 10 filtered coefficient reorganized matrixes, wherein “∥” is an absolute value sign; {circle around (1)}-8 selecting filtered DCT coefficients in each filtered coefficient reorganized matrix respectively corresponding to L org and R org which are greater than the first sensitivity threshold T1 to be determined as visual sensitivity coefficients, calculating proportions of visual sensitivity coefficients in each filtered coefficient reorganized matrix respectively corresponding to L org and R org , denoting a proportion of visual sensitivity coefficients in an n′ th filtered coefficient reorganized matrix S L,org n′ corresponding to L org as P r L (n′), wherein P r L (n′)=R T L (n′)/R L (n′), denoting a proportion of visual sensitivity coefficients in an n′th filtered coefficient reorganized matrix S R,org n′ corresponding to R org as P r R (n′), wherein P r R (n′)=R T R (n′)/R R (n′), wherein R T L (n′) represents a number of visual sensitivity coefficients in the n′ th filtered coefficient reorganized matrix S L,org n′ corresponding to L org , R L (n′) represents a total number of filtered DCT coefficients in the n′ th filtered coefficient reorganized matrix S L,org n′ corresponding to L org , R T R (n′) represents a number of visual sensitivity coefficients in the n′th filtered coefficient reorganized matrix S R,org n′ corresponding to R org , and R R (n′) represents a total number of filtered DCT coefficients in the n′th filtered coefficient reorganized matrix S R,org n′ corresponding to R org ; {circle around (1)}-9 processing quantization coding on the average value and the standard deviation of the absolute value matrix of the difference value of each coefficient reorganized matrix corresponding to L org and each coefficient reorganized matrix corresponding to R org for serving as a first digital watermarking information; processing quantization coding on a proportion of the visual sensitivity coefficients in each filtered coefficient reorganized matrix corresponding to L org for serving as a second digital watermarking information; processing quantization coding on a proportion of the visual sensitivity coefficients in each filtered coefficient reorganized matrix corresponding to R org for serving as a third digital watermarking information; utilizing a dither modulation digital watermarking embedding method, respectively embedding the first digital watermarking information into a fourth coefficient reorganized matrix S L,org 4 corresponding to L org and a fourth coefficient reorganized matrix S R,org 4 corresponding to R org , respectively embedding the second digital watermarking information into a fifth coefficient reorganized matrix S L,org 5 corresponding to L org and a fifth coefficient reorganized matrix S R,org 5 corresponding to R org , respectively embedding the third digital watermarking information into a sixth coefficient reorganized matrix S L,org 6 corresponding to L org and a sixth coefficient reorganized matrix S R,org 6 corresponding to R org , in such a manner that a stereo image with digital watermarking is obtained; {circle around (1)}-10 sending the stereo image with digital watermarking to a receiving terminal by the transmitting terminal; {circle around (2)}-1 at the receiving terminal, denoting a received distorted stereo image with digital watermarking for evaluating as S dis , S dis is a distorted stereo image of S org , denoting a left-view image of S dis as L dis , denoting a right-view image of S dis as R dis ; dividing L dis and R dis respectively into M × N 8 × 8 image blocks which are non-overlapped with each other and have a size of 8×8, wherein M is a width of L dis and R dis , N is a height of L dis and R dis ; {circle around (2)}-2 processing discrete cosine transform (DCT) on each image block in L dis and R dis , so as to obtain a DCT coefficient matrix of each image block in L dis and R dis ; {circle around (2)}-3 processing coefficient reorganization on all DTC coefficients in the DCT coefficient matrix of all of the image blocks in L dis and R dis , so as to obtain 10 coefficient reorganized matrixes which are different from each other and respectively corresponding to L dis and R dis , denoting an n′th coefficient reorganized matrix corresponding to L dis as S L,dis n′ denoting an n′th coefficient reorganized matrix corresponding to R dis as S R,dis n′ , wherein DCT coefficients having a same coordinate position in the DCT coefficient matrixes of all the image blocks in L dis are located in a same coefficient reorganized matrix, and DCT coefficients having a same coordinate position in the DCT coefficient matrixes of all the image blocks in R dis are located in a same coefficient reorganized matrix, wherein 1≦n′≦10; {circle around (2)}-4 calculating an absolute value matrix of a difference value of each coefficient reorganized matrix corresponding to L dis and each coefficient reorganized matrix corresponding to R dis , denoting an absolute value matrix of a difference value of an n′ th coefficient reorganized matrix S L,dis n′ corresponding to L dis and an n′ th coefficient reorganized matrix S R,dis n′ corresponding to R dis as D dis n′ , denoting an lth DCT coefficient of D dis n′ as D dis n′ (l), wherein D dis n′ (l)=|S L,dis n′ (l)−S R,dis n′ (l)|; calculating an average value and a standard deviation of the absolute value matrix of the difference value of each coefficient reorganized matrix corresponding to L dis and each coefficient reorganized matrix corresponding to R dis , respectively denoting the average value and the standard deviation of D dis n′ as μ d n′ and σ d n′ , wherein μ d n ′ = 1 L n ′ ∑ l = 1 L n ′ D dis n ′ ( l ) , σ d n ′ = 1 L n ′ - 1 ∑ l = 1 L n ′ ( D dis n ′ ( l ) - μ d n ′ ) 2 ; wherein S L,dis n′ (l) represents an lth DCT coefficient in S L,dis n′ , S R,dis n′ (l) represents an l th DCT coefficient in S R,dis n′ , wherein “∥” is an absolute value sign, 1≦l≦L n′ wherein L n′ represents a total number of DCT coefficients in S L,dis n′ or S R,dis n′ ; {circle around (2)}-5 respectively processing filtering on all of the DCT coefficients in the DCT coefficient matrix of each image block in L dis and R dis utilizing Watson sensitivity operator, so as to obtain a filtered DCT coefficient matrix of each image block in L dis and R dis ; {circle around (2)}-6 respectively processing coefficient reorganization on the DCT coefficients of the filtered DCT coefficient matrix of all the image blocks in L dis and R dis utilizing the same way of coefficient reorganization as thereof in the step {circle around (2)}-3, so as to obtain 10 filtered coefficient reorganized matrixes which are respectively corresponding to L dis and R dis , and different from each other, denoting an n′th filtered coefficient reorganized matrix corresponding to L dis as S L,dis n′ , denoting an n′th filtered coefficient reorganized matrix corresponding to R dis as S R,dis n′ , wherein filtered DCT coefficients having a same coordinate position in the filtered DCT coefficient matrixes of all the image blocks in L dis are located in a same filtered coefficient reorganized matrix, and filtered DCT coefficients having a same coordinate position in the filtered DCT coefficient matrixes of all the image blocks in R dis are located in a same filtered coefficient reorganized matrix, wherein 1≦n≦10; {circle around (2)}-7 according to all of the filtered DCT coefficients in the 10 filtered coefficient reorganized matrixes respectively corresponding to L dis and R dis , calculating a second sensitivity threshold, which is denoted as T2, wherein T 2 = α × ∑ k = 1 10 ∑ l = 1 L k  S dis _ k ( l )  / ∑ k = 1 10 L k , wherein α is a sensitivity threshold regulatory factor, 1≦k≦10, 1≦l≦L k , wherein L k represents a total number of filtered DCT coefficients of a k th filtered coefficient reorganized matrix in the 10 filtered coefficient reorganized matrixes respectively corresponding to L dis , or R dis , wherein S dis k (l) represents an l th filtered DCT coefficient of a k th filtered coefficient reorganized matrix in the 10 filtered coefficient reorganized matrixes respectively corresponding to L dis or R dis , wherein “∥” is an absolute value sign; {circle around (2)}-8 selecting filtered DCT coefficients in each filtered coefficient reorganized matrix respectively corresponding to L dis and R dis which are greater than the second sensitivity threshold T2 to be determined as visual sensitivity coefficients, calculating proportions of visual sensitivity coefficients in each filtered coefficient reorganized matrix respectively corresponding to L dis and R dis , denoting a proportion of visual sensitivity coefficients in an n′ th filtered coefficient reorganized matrix S L,dis n′ corresponding to L dis as P d L (n′), wherein P d L (n′)=D T L (n′)/D L (n′), denoting a proportion of visual sensitivity coefficients in an n′th filtered coefficient reorganized matrix S R,dis n′ corresponding to R dis as P d R (n′), wherein P d R (n′)=D T R (n′)/D R (n′), wherein D T L (n′) represents a number of visual sensitivity coefficients in the n′th filtered coefficient reorganized matrix S L,dis n′ corresponding to L dis , D L (n′) represents a total number of filtered DCT coefficients in the n′th filtered coefficient reorganized matrix S L,dis n′ corresponding to L dis , D T R (n′) represents a number of visual sensitivity coefficients in the n′ th filtered coefficient reorganized matrix S R,dis n′ corresponding to R dis , and D R (n′) represents a total number of filtered DCT coefficients in the n′ th filtered coefficient reorganized matrix S R,dis n′ corresponding to R dis ; {circle around (2)}-9 detecting a first digital watermarking information embedded in S dis , processing decoding and inverse quantization on the detected first digital watermarking information, so as to obtain an average value and a standard deviation of the absolute value matrix of the difference value of each coefficient reorganized matrix corresponding to L org and each coefficient reorganized matrix corresponding to R org embedded at the transmitting terminal, processing texture similarity measurement on S dis utilizing Canberra distance, so as to obtain a stereo perception value of S dis , which is denoted as Q disp , wherein Q disp = ∑ n ′ = 1 10 w n ′ (  μ r n ′ - μ d n ′  +  σ r n ′ - σ d n ′  ) ∑ n ′ = 1 10 w n ′ ( μ r n ′ + μ d n ′ + σ r n ′ + σ d n ′ ) , wherein μ r n′ and σ r n′ respectively represent a average value and a standard deviation of absolute value matrix of the difference value of an n′ th coefficient reorganized matrix S L,org n′ corresponding to L org and an n′ th coefficient reorganized matrix S R,org n′ corresponding to R org embedded at the transmitting terminal, wherein w n′ represents a weight, w n ′ = { 1 , if n ′ = 1 0.5 if n ′ = 2 or n ′ = 3 or n ′ = 4 0.25 , if n ′ = 5 or n ′ = 6 or n ′ = 7 0.125 , if n ′ = 8 or n ′ = 9 or n ′ = 10 , “∥” is an absolute value sign; detecting a second digital watermarking information embedded in S dis , processing decoding and inverse quantization on the detected second digital watermarking information, so as to obtain a proportion of visual sensitivity coefficients in each filtered coefficient reorganized matrix corresponding to L org embedded at the transmitting terminal, then calculating a left-view quality value, which is denoted as Q view L , wherein Q view L = 1 1 + log 2 ( K L Q 0 + 1 ) , wherein Q 0 is a dynamic adjustor, K L = ∑ n ′ = 1 10  P r L ( n ′ ) - P d L ( n ′ )  , wherein P r L (n′) represents a proportion of visual sensitivity coefficients in an n′th filtered coefficient reorganized matrix S L,org n′ corresponding to L org embedded at the transmitting terminal, “∥” is an absolute value sign; detecting a third digital watermarking information embedded in S dis , then processing decoding and inverse quantization on the third digital watermarking information detected, so as to obtain a proportion of visual sensitivity coefficients in each filtered coefficient reorganized matrix corresponding to R org embedded at the transmitting terminal, then calculating a right-view quality value, which is denoted as Q view R , Q view R = 1 1 + log 2 ( K R Q 0 + 1 ) , wherein K R = ∑ n ′ = 1 10  P r R ( n ′ ) - P d R ( n ′ )  , P r R ( n ′ ) represents a proportion of visual sensitivity coefficients in an n′th filtered coefficient reorganized matrix S R,org n′ corresponding to R org embedded at the transmitting terminal; {circle around (2)}-10 calculating a view quality value of S dis according to Q view L and Q view R , which is denoted as Q view , wherein Q view =(Q view L +Q view R )/2; {circle around (2)}-11 calculating an objective quality score of the distorted stereo image S dis utilizing a support vector regression model with an optimal weight vector W opt and an optimal bias b opt , denoting the objective quality score of the distorted stereo image S dis as Q obj , Q obj =(W opt ) T φ(x)+b opt , wherein x=[Q disp ,Q view ], x represents a vector constituted by the stereo perception value and the view quality value of the distorted stereo image S dis , (W opt ) is a transposed vector of W opt , φ(x) is a linear function of x.