File info response includes a value of a perceptual hash calculated using pixel contents of an image. Perceptual hashing is a common fingerprinting technique to quickly compare images and find duplicates or similar images. Uploadcare automatically calculates a 64-bit long perceptual hash value and returns it as a HEX string. It’s easy to find image duplicates by quickly comparing their perceptual hash values. To find similar images, it’s important to compare perceptual hash values bitwise (Hamming distance). A small number of unmatched bits (e.g., up to 8 bits) will correspond to subtle changes in the visual contents, while non-similar images will usually have more than 8 different bits.