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

I'd suggest a tagging system similar to the one here on stackoverflow. Allow them to tag the images, then view by tag, or combination of tabs. When viewing the page, show thumbnails of the images and the tags for that image below it.

Edit: Based on your clarifications you could have types of tags. When the user defines their own tag, they would need to specify which type it derivies from. With that in mind, you would need limit tags to only one of that type.

TagType { Color, Seats, BodyType, Seats }
TabSubType { Color-Red, Color-Blue, Color-Green, Seats-2, Seats-4, ... }

When a user wants to add tag an image give them a drop down with the TagType. Below that give then another drop down with the TabSubTypes. Give them an option to "Define New" which will cause a textbox to appear where they can type in a new type.

I'd also add these options to the context menu so users can view the tags in a tree style menu. You could also grab the keypress even when an image is focused, look up the TagType and TagSubType name and present a menu of options to choose from. If no matches are found, offer a "Click to add new tag" option.