I wish I knew. There was some speculation on the live thread starting
here.
Rep. Weldon was one of the last to question Secretary Rumsfeld. Even Fox News had cut from the testimony at that time.
I don't think Secretary Rumsfeld responded to the question.
We also know from General Myers' response to a question from Senator Sessions that soldiers accused in the Taguba report had access to it for rebuttal purposes. As I understand it, the report can be used not only as a springboard to court marshall, but also to admonish the accused soldiers in other ways. It's not clear whether they also had access to the pictures. Maybe someone who is familiar with military law could explain.
If you beleive Hillary! slipped up and stated that she had access to the actual Taguba report before the Pentagon, perhaps this staffer was the leaker.
But this is all just speculation.