@clarkesworld A few thoughts: You are dealing with a special kind of spam here, call it slop spam. To catch a spammer, remember they are lazy people. They don't fake meta data well, or don't even bother.
Look at repetitive patterns in IP addresses or user agents of the submitting Browser.
don't accept submissions from outdated software, like a ten year old firefox.
don't accept submissions by people that don't bother to hide they are using curl or wget. #spam#slop#ai 1/3