@Lyne....
You said**...."I don't think watermarking the compressed art we post (that can't really be printed well anyway)"

**Unfortunately that is not the case anymore...there is very good "upresing" software available on the market now.  Depending on the image, upsizing of 4 to 8 times is reasonable...which would turn your 800x600, or 1024x768 into a nice print.

Prints of ripped images are being sold in many parts of the world right now....

Sadly, your only solution is to heavily watermark. post very very small...or...not upload.  Generally rippers will not bother to try to defeat a heavy watermark...it is quicker for them to go steal another image that has none....

BTW, the site in question was posted in the copyright forum 3 months ago....obviously nothing has been removed since then.

In youth, we learn....with age, we understand.