Well, from the post Akar linked to, apparently it needs to be stated explicitly that search queries based on what can be seen by a human are ok, but using computer algorithms operating on the images themselves are not. In other words, that efforts to thwart reverse image search are there to avoid cheating and are not in themselves the challenge. Yeah I know, seems blatantly obvious .....
Having said that, I think 'guess the historical figure' is perhaps the worst guess game on this forum, as images are usually devoid of clues other than an indication of the period. It's more like "you know it or you don't" than a guess.