You are badly confusing publishing with copyrights. Most photographers like their work published. Some publish through art galleries, some through newspapers, s

You are badly confusing publishing with copyrights. Most photographers like their work published. Some publish through art galleries, some through newspapers, some through billboards, and some through twitter. None of these make it public domain, however. Public domain means anyone can use the photo as they see fit, which is not why the photographer put it out there. She is exercising her copyrights by licensing the photo (royalty free) to whatever service she uploaded it to. (It's always in the ToS that by uploading, you give them some sort of license, but you usually do not give them the copyright.) Now, it is possible that she uploaded to Twitpic, which specifies in its ToS that by uploading, you give them license to publish and relicense the photo. If that's the case, then it is possible the various news agencies went to Twitpic to get a license to use the photo (for free or for some fee paid to Twitpic), but my guess is that is not what happened. Think of it this way: if you wrote a book and posted a link to it on twitter, would you be happy if someone else started selling it on Amazon?