A method of detecting image format includes dividing a single-frame image into a plurality of macro-blocks; calculating a correlation coefficient of a left-half image of the single-frame image and a right-half image of the single-frame image as a first global similarity; calculating a correlation coefficient of a top-half image of the single-frame image and a bottom-half image of the single-frame image as a second global similarity; calculating a portion difference of each macro-block; comparing the portion differences of the left-half image and the right-half image, for acquiring a first local similarity; comparing the portion differences of the top-half image and the bottom-half image, 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.