[pedalpete]

I should think you could do this with fingerprinting the photo similar to how music is fingerprinted for things like Shazam or MusicBrainz. I used to work for MusicIP, which I believe developed the fingerprinting system MusicBrainz is using.

[wgrover]

Thanks for the suggestion - I looked into music recognition algorithms early on but struggled to adapt them for image use. But I'll revisit them.

[rkagerer]

Are there "fuzzy" fingerprint algorithms that tolerate some variation in pixel color / hues, edges, imaging quality, etc?

[kevindamm]

There are image-representation versions of wavelets that would work well in that context, with some tolerance/quantization of the frequency representation to accommodate fuzzy edges, and likewise for nearby hues.

Perceptual color representation gets a bit harder but if you're only looking at gamut differences on cameras/screens/printed media I think it's feasible.

Alternatively, if you know a lot about the source image you can train a NN for the specific application.