@Karen -[Is WordPress] really usable if you have a lot of photos or media that needs to be organized by groups or folders?

This is a favorite challenge of mine, too. And, although he is better known for his musical interests, WP founder Matt Mullenweg also is a serious shutterbug. He has a photo collection well up into 5 figures, and has struggled "publically" with how to manage them.

The direct & honest answer to this question ('How useful..'), in a nutshell, for you, me & Matt, is 'Not very' ... tho by thinking outside the box, and being flexible, 'oneself' (instead of insisting that the key flexibility is in the tool), useful approaches/solutions can be had.

Number one on my wish list would be flexibility & options in how I can organize my media.

WordPress achieves or is able to offer "flexibility & options", primarily through plugins (and sorta through themes ... of which there are 'photo-blog' types (etc) specifically aimed at the 'images problem').

WP itself might offer 'some' solution (in any given area), but offering a 'pick & choose' or 'mix n match' array of solutions is usually going to be left to plugins.

There are plugins that (try to/purport to) offer what you ask for. And they do it in different ways, using different strategies. I have installed several of them and looked at their Admin interfaces and database tables.

But again, the honest truth is that the general idea of 'organizing' images is a tough nut, even for such entities as the CIA and FBI. Our military and Pentagon struggle valiantly with the same media-issues that confront us. Hollywood quietly pulls their hair out.

It is said that in any challenge or confrontation, the first step should be to "Know the enemy". Just what are we actually 'up against', when we set out to organize photographs?