[venturi]

Ditto to what Spaz said. As far as using the thumbs goes though, there are at least a half dozen different "standard" sizes that the various TGPs want submitted to them, not to mention all the quirky variations that abound. The majority of "full-time" gallery submitters generally do their own thumbs anyway for a variet of reasons ranging from needing multiple sizes to wanting very specific shot types and quality levels, etc. etc. I know a few submitters that literally will spend 10 to 15 minutes per thumb to get just the right color correction, gamma, etc. for their thumbs so that they get that tiny bit of edge in perceived quality to hopefully get a few extra clicks over the other guy.

And Jace is right on the mark too. Hosted Gallery servers burn a massive amount of traffic - hundreds of mbit per sec. Hotlink protection can save a boat load of money for the sponsor just on BW alone, not to mention having to police content thieves that just want to rip your thumbs to pad their traffic scams - and watermarking thumbs is akin to trying to teach a pig to sing...