It's been my (empirical) experience that some people have a better visual memory, and other people have a better memory for concepts and words--and of course, some lucky people are good at remembering both. I know that I have a lot of trouble remembering strictly visual information, or even visualizing something I've seen before. But I memorize numbers, quotations, passwords, and things like that without even intending to.

This is why I kind of hate standardized tests; they fail to take into account the fact that different people think in different ways. I think I'm fortunate to have grown up at a time when (in my country, at least) standardized tests weren't especially popular in educational circles, so I don't recall having to take many as a kid.