1. A method of automatically detecting image formats, comprising: dividing a single frame image into a plurality of first macro-blocks; calculating a correlation coefficient between a plurality of image features of a plurality of first left macro-blocks and a plurality of image features of a plurality of first right macro-blocks as a first global similarity, wherein a first left macro-block is the macro-block of the plurality of first macro-blocks belonging to a left-half image of the single frame image and a first right macro-block is the macro-block of the plurality of first macro-blocks belonging to a right-half image of the single frame image; calculating a correlation coefficient between a plurality of image features of a plurality of first top macro-blocks and a plurality of image features of a plurality of first bottom macro-blocks as a second global similarity, wherein a first top macro-block is the macro-block of the plurality of first macro-blocks belonging to an upper-half image of the single frame image and a first bottom macro-block is the macro-block of the plurality of first macro-block belonging to a lower-half image of the single frame image; calculating a portion difference of each first macro-block according to the image feature of each first macro-block; comparing the portion difference of each first left macro-block and the portion difference of the corresponding first right macro-block for acquiring a first local similarity; comparing the portion difference of each first top macro-block and the portion difference of the corresponding first bottom macro-block for acquiring a second local similarity; and detecting an image format of the single frame image according to the first global similarity, the second global similarity, the first local similarity, the second local similarity, a first threshold and a second threshold.