If you see someone posting in different contests, you can usually tell. Sometimes they will make the mistake of posting a so-so out of focus and badly lit shot, and the next minute they are entering complicated shots that use multiple studio lights, or something like that. Often too, I simply recognize a lot of stock shots, because I have been submitting for over 20 years and know a lot of the photographers! Sometimes they even fake camera settings, and put in something that would make absolutely no sense for the photograph. LOL!