Posting screen captures in game chat

Is it against the rules to post a link to a screen capture of the game being played in the game chat? Basically I pointed out a strategy that an opponent was using (without calling out specifically who it was) about 10 rounds back, and the person who was using that tactic is all indignant that he would never do that. I've got the proof that he did. It's not a Fog game (even if it wasn't expressly forbidden, that would be out of bounds of fair play, IMO), so the information in the screen caps would have been available to all players at the time, if they had been paying attention.