Width and height aren't strictly required but they're almost always nice to have. They can slightly speed up rendering since the browser can flow text around an image before the image has finished downloading, though that's probably not a huge concern here. But there's no reason to remove them either.

I think the correct license is 'Creative Commons - Attribution-NonCommercial-ShareAlike'.

We should add the same string as the alt in a title attribute as well, so it appears in a tooltip to explain what the image means.

You can also add 'license' to that rel attribute for some extra microformatty goodness (rel="external license").