An image similarity determining device and method and an image feature acquiring device and method are provided. The image similarity determining device comprises a preprocessing unit for extracting feature points of each input image region of an input image and each image region to be matched of a data source image; a matched feature point set determining unit for determining one to one matched feature point pairs between input image regions and image regions to be matched to determine matched feature point sets; a geometry similarity determining unit for determining a geometry similarity between the input image region and the image region to be matched based on distribution of respective feature points in the matched feature point sets; and an image similarity determining unit for determining similarity between input image and data source image based on geometry similarities between input image regions and corresponding image regions to be matched.