Pretty links for attachments without posts/pages?

Hi all,
I have activated mod_rewrite and pretty links, it works fine for everything except attachments. I found out that obviously pretty links only work for an attachment if it is linked to a post or page.

That’s exactly my problem, I have a nice image.php file to display single attachements which works fine – however, I don’t want a link like http://mysite.com/?attachment_id=123 – at least i’d like to read it something like http://mysite.com/photographs/123, even better but probably impossible without a suitable plugin http://mysite.com/images/title-of-image or http://mysite.com/images/category/title-of-image. However, I still want to use the built in media library.

Does anyone know a plugin solving this issue or how to write such an mod_rewrite rule for my .htaccess?