Martin's first picture

Well, one of the key themes in the film is trust, and Martin's difficulty trusting others. But Andy can't have known how Martin's mother described the scene Martin photographed as a child. We learn about it in flashback. Andy has been the only character in the film Martin trusted until Celia intervenes; after this Martin impulsively seeks isolation again. Andy tells him he has to learn to accept imperfection in others, that they're all human and that sometimes you just have to trust them without "proof". Andy is a basically honest person. He doesn't even conceal the affair with Celia very long.

But in some sense, Andy's description of the photograph gives Martin the proof he's been searching for since childhood, the proof that his mother, though not overly demonstrative, did tell him the truth and did care about him. The irony is that Martin has to trust Andy to finally have his proof. Before this, Martin never trusted WITHOUT proof. The film does reward repeat viewings. I still need to take the time to watch the DVD director commentary version.