May have just been lost in the pile of evidence and other photos. Too bad, he could have used this from day one. hopefully this will make the "not guilty" verdict come a bit easier.
Edit:
Sounds like the prosecutors office was sitting on it though...probably because it would have blew their bogus murder charges out of the sky
From the article: "O'Mara told Reuters that prosecutors in May had given him a grainy black-and-white photocopy of the image which was taken in the back seat of a Sanford police cruiser. O'Mara said he received the digital image from prosecutors after repeated demands by his office and he posted it Monday on Zimmerman's defense website."