Most elegant UI for categorizing items?

Question

I have a collection of items that the user needs to group/categorize in several ways. For the sake of an example, let\'s say it\'s a collection of cars and the user wants to cat

Answer 1

You could use tags: Have the user tag each image, then show a set of image thumbnails sorted by tags.

Maybe more advanced than tags would be a set of user-defined attributes. For example, instead of tagging a picture with "red", tag it with an attribute "color=red".