1. An image processing method for detecting visual saliency of an image based on regional contrast, the method comprising: segmenting an input image into a plurality of regions by using an automatic segmentation algorithm; and calculating a saliency value of one region of the plurality of segmented regions by using a weighted sum of color differences between the one region and all other regions and by using spatial distances between the one region and all other regions, wherein, in the segmenting, a saliency S(r k ) of a region r k of the plurality of segmented regions is defined by the following expression: S ⁡ ( r k ) = ∑ r k ≠ r i ⁢ exp ⁡ ( - D s ⁡ ( r k , r i ) σ s 2 ) ⁢ w ⁡ ( r i ) ⁢ D c ⁡ ( r k , r i ) , and wherein D s (r k ,r i ) and D c (r k ,r i ) are respectively a sMatial distance and a color difference between the region r k and a region r i , and k are natural numbers, w(r i ) is a weighted value of the region r i and σ s 2 is a parameter for controlling the effect of a distance factor.