You WANT it to be distributed and concede the necessary rights to TwitPic, but that's very different from putting it out in the public domain. You still retain copyright, and normally the picture host shouldn't be able to sell it nor journalists to use it (this is precisely the reason there was such a kerfuffle about the TwitPic TOS recently).

I hate being self-promotional, but this issue is exactly the reason we created Picuous, which is a Vimeo/SoundCloud/Scribd for pictures: pictures can be embedded legally, carry automatic attribution, and can be tracked by the picture owner. Using the pictures in the player is free, using them in other contexts is pay-for.

We want to change this traditionnal diffusion/monetization/ownership Bermuda Triangle… People interested in this problem should check it out: http://picuous.com. All feedback is welcome on martin@picuous.com.