1. An image similarity determining device for determining similarity between an input image and a data source image, the image similarity determining device comprising: a preprocessing unit configured for dividing the input image into at least one input image region and dividing the data source image into at least one image region to be matched, and extracting feature points of each input image region and each image region to be matched; a matched feature point set determining unit configured for determining, with respect to each input image region, one to one matched feature point pairs between the input image region and each image region to be matched, according to the feature similarities between each feature point of the input image region and each feature point of respective image regions to be matched, and forming a matched feature point set including all the matched feature points for the input image region and its corresponding image regions to be matched according to the one to one matched feature point pairs; a geometry similarity determining unit configured for determining, with respect to each input image region and its corresponding image region to be matched, a geometry similarity between the input image region and the corresponding image region to be matched, based on the distribution of respective feature points in the matched feature point set of the input image region and the distribution of respective feature points in the matched feature point set of the corresponding image region to be matched; and an image similarity determining unit configured for determining the image similarity between each input image region and its corresponding image region to be matched, according to the geometry similarity between the input image region and the corresponding image region to be matched, and determining the similarity between the input image and the data source image according to the image similarities between each of the input image regions of the input image region and respective corresponding image regions to be matched.