I'm fine with trusting users who look like they deserve it. They are, after all, the ones affirming the copyright status of the image; unless I have a really good reason to doubt them I'm going to go with their call on these things.
Bots obviously lack such ability for judgment, unless they are human-augmented.
I'd even be fine with trusting an editor who hasn't been around a while, if the rest is plausible. But something like "anonymous" without further comment makes it look like "couldn't be bothered". Not knowing the bot, I'd have to guess it keys into exactly that word.
Dan