Probably not what you have in mind, but Org-mode can do it (more or less). And if there's a place this is implemented already (or will be soon), I would bet on

Probably not what you have in mind, but Org-mode can do it (more or less). And if there's a place this is implemented already (or will be soon), I would bet on DrRacket. Still, an interesting idea. I'm more of a text guy than a visual learner, but I agree that comments in the form of images could be very useful. The problem I can envision with this is that whoever adds such a feature to some IDE/environment would probably run with it and add sound and video comments, too, and then it will be like XML: making sense in theory, but horribly abused 99% of the time...