FWIW, I originally proposed in forum #130737 to use IQDB to validate that the image being replaced at least matches the current image in similarity.
This would stop malicious replacements but things like revisions or Twitter -> Pixiv replacements would still pass this check.
RaisingK said:
Perhaps make a separate "can replace posts" permission?
It's less a hassle to implement than it is to manage. If we go down this road until everyone has five or ten separate permissions for different things, it will become difficult to track just who can do what.
It also raises questions of who will give out these permissions (currently only one mod promotes anyone at all), and who should be chosen. Or to put it another way: which approvers should not be chosen, and how can we trust them with anything if we can't trust them with this simple job?
To be honest I think we should just give RaisingK and BrokenEagle mod accounts for their bots and let them automate replacements, assuming they are so inclined.