I'm also unsure, but either it's pure human, a human behind the machine, or a bot that will actually read and process images. Either way, that's higher effort than most bots on SN haha.

Also, if you're human @Sandusky I hope it doesn't offend you. We've had a big bot problem on SN and you can understand why bounties for math puzzles are an especially sensitive area for bot policing.