It’s the author of the article. I don’t think Snapzu’s algorithm is the best when it comes to choosing pictures of an article.
Fashioning a snap picture is up to the submitter. Snapzu's Submit button and SnapIt! bookmarklet will extract an image for the draft, but agreed, it doesn't do the job an interested poster would. While a snap without a picture may not get very far, there are four snaps on the front page right now with snap pictures that were clearly, variously neither selected, edited nor framed by hand. Someday, I imagine, Snapzu users will use snap pictures far more capably than they do now.
For me, sometimes half the fun is finding a pithy pic if the Snapzu system doesn't sweep up a good one.