SHA hashes aren’t suitable for this: you can change a single bit in the header to bypass a hash check. Perceptual hashes are designed to survive cropping, rotation, scaling, and embedding but all of those things mean that false-positives become a concern. The real risk would be if someone figured out how to many plausibly innocent collisions where you could send someone a picture which wasn’t obviously contraband or highly suspicious and attempt to convince them to save it.