media tagging possibilities

I’m building a website using WordPress (essentially using WP as a CMS), and I’ve come across a problem with handling large amounts of pictures. What I actually need is support for adding tags to images and then being able to query tagwise for collections of images, so I can display them freely on the website.

I’ve been wading through the interwebs to find a plugin that will let me do this, but no luck so far. Can anyone tell me whether something like this exists, and if not, how hard it would be to build?

Thanks in advance!