Deriving randomness from picture(s) isn't a bad idea, and it's a feature of SeedSigner, if I remember correctly.
Using it for backup is tricky, as was mentioned. I can definitely see people taking screenshots of the relevant pictures or sending them via a messenger, which in 99% of cases alters the image hash.
As for remembering 'which image it was', it can be actually 'hidden in plain sight' like printing it out and keeping it in your wallet or hanging it on a wall. But you definitely need to be able to retrieve the actual file from which the randomness was generated and I'm not sure how to accomplish it. Maybe you could zip up like 1000 pictures and upload that to cloud storage and keep a reference (to find the right one again) printed on a wall. If needed, download the zip and unpack it, that should return the original 1000 images and then pick the right one to restore your wallet.
Something like this should pretty surely work. You can upload that zip to many places, copy it to a few hard drives and such. Especially if this is not a commonly used / standardized procedure, this 'security by obscurity' might work nicely.

Only issue is as with all 'custom crypto' (don't roll your own crypto), if let's say you pass away and your family knows nothing about this scheme, they won't randomly think to unzip that file, take the image that is hung in your office and pass it through a program from GitHub to restore a Bitcoin wallet.
Instead, if they find some paper with 12 words, they might look online and find out this is a Bitcoin wallet seed.