Steph, have you tried one of those USB camera's? The lens might be small enough to poke through the mesh, should give you some depth between the marble and the mesh so it's not on the same plane of focus. I'm the same way with a couple mesh bags I have, can barely see the marbles clear let alone take a pic.
Side-note: I was going through marbles a couple days ago, this thread came to mind and I decided I'm perfectly OK with not being to ID swirl marbles. It's a challenge