As I stated in the 'spam comments' post:
"One way to prevent the auto guest post is, 1- prevent auto guest posting by requiring the artist to create an account, in turn, have said artist submit a number of artwork pieces before they can comment on other work.
2- moderate all comments, this delays the appearance of the comment."
The #1 opt worked well at a writing website where I'm a member. We could not comment on someone's writing until we submitted five posts of our own. Then, we had to wait 7 days before commenting/replying to comments/critiques on our own writing.
Perhaps this can be arranged somehow.
I'm sure there are many of us here, that would help 'volunteer' to ensure our website here is safe.