Perceptual hash (phash)
An image fingerprint pinned into a certificate to tie it to a specific picture of the work.
A perceptual hash summarises what an image looks like into a short fingerprint, so two near-identical images produce near-identical hashes. It lets a certificate commit to a particular photograph of a work and detect if that image is swapped for another.
It is a strong, work-level fingerprint for flat media — painting, drawing, photography, works on paper — but it degrades for three-dimensional and textile work, where a photograph captures only one angle. For those media, and for editioned works where every copy shares one image, identity rests on the registry and attestation rather than the image fingerprint. Attesian is deliberate about not overselling it.