The current screenshot of the day ( http://www.gamedev.net/page/showdown/view.html/_/octoman-r164215 ) has been featured many times now.

Looking at the history, it seems to be because the same image is posted and tagged multiple times, so it think it's a unique image -- fair enough.

Blocking the user might be a bit harsh, but is there anything that could be done about this, to avoid seeing the same image tens of times during the same month?

Especially when the image in question is advertising/selling stuff, it just feels very off to me as it currently stands.

Bump since it's back again.

seems more of an ad to me. Perhaps pulling these from twitter isnt the best of moves considering how many abuse that platform to spam?

This is a known issue and being addressed.