Algorithmic solutions will always be hard. "I know it when I see it" is hard to program. Depending on the site, I'd go to a trust-based solution. New users get

Algorithmic solutions will always be hard. "I know it when I see it" is hard to program. Depending on the site, I'd go to a trust-based solution. New users get their images approved by a human censor (pr0n == spambot in most cases). Established users can add images without approval. If you're going to try software, try something that errs on the side of caution, and send everything to a human for final decision-making, just like spam filters.