imgur
Can I add an image uploaded to Imgur by someone else to my Imgur account without re-uploading it?
I like to keep a collection of images in my Imgur account that I find interesting, all of which show up at http://<username>.imgur.com/all/. However, it seems wasteful to use Imgur in order to rehost images that are already hosted on Imgur.
From the TOS, this would seem to suggest that nothing happens to your licensing.
Imgur Terms of Service are subject to change without notice. All files are copyrighted © to their respective owners. Imgur directs full legal responsibility of files to their respective users.
To answer the other part of your question, AFAIK, there is now way to associate any particularly licensing information to an image hosted on imgur. IANAL, but it sure seems like this should mean that nobody has any rights to your image, other then what is needed to view it while it is hosted on imgur. It seems to me that you could link to the image from a blog or something and spell out any particular rights or license that you wish to use for use beyond viewing on imgur.
I can't actually find it documented anywhere, but I uploaded an image and played with the "More Sizes" list:
http://i.stack.imgur.com/YdJZt.jpg
I haven't included the image inline, because StackExchange would automatically scale it down. To view the original at its full size, click the link.
http://i.stack.imgur.com/YdJZtl.jpg (added an l after the image ID)
http://i.stack.imgur.com/YdJZts.jpg (added an s after the image ID)
It doesn't always handle transparency well, but "small square" is probably what you want.
Image by digitalART2, licensed under CC-BY-2.0, available here.
Best Answer
The favourite button allows you to keep all favourited pictures in a "favourites" album. It is a small heart icon near the upvote and downvote buttons. The hotkey is numpad 0.