I decided to respond. I am sick of just letting this kind of shit slide and hoping gross dudes will disappear. I also wanted it to be clear that this was unwanted, for posterity, in case this turns into something worse. So that I can say with proven confidence that I was not in any way encouraging this.

My response: "Solid NO. And just so we're clear, do not send me any more unsolicited pictures. That's harassment, dude, and if you do it again, I will treat it as such."

I feel instantly better.