Perceptual Hashing

A technique that generates a compact fingerprint (hash) of an image based on its visual content rather than its raw data. Unlike cryptographic hashes that change completely with any modification, perceptual hashes produce similar values for visually similar images, allowing efficient detection of duplicate or near-duplicate images. In accessibility and crowd-AI systems, perceptual hashing reduces costs by reusing previous labels for unchanged or nearly identical images instead of sending them to human workers for re-labeling.