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.
Sean 
Art Deco,
As for the former supposition, if he were truly alarmed by Zimmerman, it is rather congruent with doing aught but getting off the street and out of the rain.
Another congruent action for an adolescent male to take is to prove his manhood by confronting his fear, rather than running from it. Another congruent action might be to circle around and try to see who this unknown follower is. Your analysis assumes a great deal. Please consider the fact that people are quite diverse, and their behavior is governed by too many factors to reliably assume we know them from this distance.
My point has to do with why a kid walking home at night was put in the position of fearing the neighborhood watchman. The job of neighborhood watchman is to make the neighborhood safe, not spook people walking alone at night.
Can we not agree that a better course of action would have been for Zimmerman to announce himself at a distance as the watchman? That would have likely defused the situation. Zimmerman, however, did not “defuse” it, he escalated it. He did this by following Martin (he followed Martin before going to his truck and making that call), and was advised to not follow Martin for precisely the reason that when amateurs do that, sometimes people get hurt, on one or both sides of the encounter. Inarguably, that is precisely what happened.
George Zimmerman made decisions that night that led to him getting into a physical altercation with, and killing, someone whose only apparent crime was walking. The “suspicious” part is in the eye of the beholder, and anyway, the police were on their way. Zimmerman’s proper course of action at that point was to wait for the cruiser to arrive, and not pursue. Do you actually deny this? Shouldn’t Zimmerman be held accountable for his role in making a non-situation into a homicide scene?