The important point is this: The anomaly in the header indicates that the image was not sent by Weiner. It had to have been sent by someone else.
Not only that. Believe it or not, when an outsider sends a pic to someone else's Yfrog account in this fashion, the action creates a message in the "twitterstream." The message seems to originate with the Twitter account holder -- but it doesn't. It comes from somewhere else -- from someone mailing a picture to the account holder.
This is a serious security flaw in the design of Yfrog and Twitter. It allows a malicious outsider to "spoof" a tweet that seems to come from someone else.
Various technical details at the link. One doubts that Rep. Weiner(D-NY) will press charges, but he would have every right to do so.