That photo was reportedly taken by a neighborhood resident three minutes after Zimmerman shot and killed Trayvon Martin. From ABC’s report:

The exclusive photo obtained by ABC News shows blood trickling down the back of Zimmerman’s head from two cuts. It also shows a possible contusion forming on the crown of his head. The original police report that night notes that the back of Zimmerman’s head was wet, and that he was bleeding from the nose and head.

Zimmerman told police that night that he shot and killed the teenager in self-defense after Martin punched him and pounced on him. Zimmerman told police that Martin then bashed his head into the concrete sidewalk during the altercation that took place in the tidy middle-class development of the Retreat at Twin Lakes in Sanford, Fla.

Zimmerman was treated at the scene by paramedics, then cuffed and driven in a police cruiser to the Sanford police station. He was questioned for hours and later released. In police surveillance video obtained last month by ABC News, Zimmerman’s wounds are not apparent, and there were no bandages on his head.

Zimmerman was not admitted to a hospital or given stitches the night of the incident.

More:

In a dramatic moment during the hearing, a detective, under questioning from [Zimmerman lawyer] O’Mara, admitted that it has no clear evidence that Zimmerman attacked Trayvon  Martin first.

I’m thinking it’s going to be extremely difficult to prove beyond a reasonable doubt that Zimmerman committed murder.