Yes. Florida has particularly favorable discovery rules for defendants in criminal cases.
-- Does Zimmerman have to let the State know what evidence they have to prove his innocence? --
Yes, the discovery obligation is mutual. But interestingly, most of the material that evidences his use of justified self defense was investigation by the police! The only witnesses that I could think of (and this is off the wall) would be his mother and brother, to testify the voice yelling "Help!" is Zimmerman - that would counterbalance Sybrina's testimony that she hears Martin.
-- Was thinking particularly of the picture taken minutes after the incident of Zimmerman's injury. If that was taken by "John", did John take other pictures? Pictures during the fight? Would O'Mara have to reveal to the prosecutor the existance of those pictures before presenting them to the Court? --
Yes, if he intends to use them. But I think it's easier for him to just use the police file and his doctor visit (handed over to the prosecutor after the bail hearing) as evidence of his injuries. But yes, anything that he intends to use in his defense, that doesn't come from the state's investigation, is turned over to the prosecution, under Florida's mutual discovery.
Florida Rules of Criminal Procedure - Rule 3.220
People speak in very unique ways...almost as identifiable as retinal scan.