Perceptual hashing
technique
Perceptual hashing boils an image down to a short code meant to match for look-alike pictures, which makes finding duplicates cheap. On retail crops it failed the job: the same product often got different codes, and different products often got the same one, because the code drops the small text and color that carry the signal.
For engineers: compact perceptual fingerprint for near-duplicate detection; loses the fine text and color cues that separate retail classes.