Thanks for the nice plugin! I especially like that the image is copied to the blog, as relying on external image links is always a risk.
However, I'd like the automatically generated caption to include the CC license. It's actually a requirement in the CC license itself that the license needs to be mentioned. Now, as there's a link to the Flickr page, it's not legally that much of a problem, but for completeness' sake it would be good to have.
So if the caption would say something like
By: AUTHOR(link to flickr), CC BY-SA(link to license page)
it would be more complete.
Please make it at least an optional feature. Or if you're too busy to implement this, I could probably spend a few moments coding that for you.