I was thinking about this last night. In terms of the evidentiary value of the photographs. Any piece of evidence which has the tendency to prove or disprove a material fact is relevant and then arguably admissible. The piece of evidence still has to be more probative than prejudicial to be admitted. Courts generally err on the side of admitting the evidence, over any challenge of being overly prejudicial, and say any challenge goes to weight not admissibility.
In terms of JM and his situation. He is alleged to be involved. He is out on bond in Florida. His friends, who I'm sure he claims he has no criminal affiliation to, are a thousand miles away, playing softball, with t shirts with his name on the front, playing another team which has the address of their social club on it. Pretty compelling evidence to me. Doesn't actually prove he committed any crime but it is pretty powerful circumstantial evidence he is involved with these guys.
In terms of all the other guys in the photos, if there is ever a prosecution against any of them, and there is a RICO or conspiracy charge these photos come in as evidence. Defense counsel can argue they are overly prejudicial and only show grown men playing in softball but I think that argument goes to the weight the jury gives the photos not whether they are admissible.
If JM didn't know bout the t shirts and the photos he should be absolutely livid. The photos look like they are challenging the Feds and the judge assigned to JMs case. Federal prosecutors and federal judges are still people with pride. These photos will not be helpful to him at all especially if he is eventually sentenced on one of the indictments.