I can't seem to find any information on what happens to my image licensing when I upload them to Imgur.
Is there any way to place my images under a certain license there?
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.
From the New TOS, everything you upload "belongs" to them:
With regard to any file or content you upload to the public portions of our site, you grant Imgur a non-exclusive, royalty- free, perpetual, irrevocable worldwide license (with sublicense and assignment rights) to use, to display online and in any present or future media, to create derivative works of, to allow downloads of, and/or distribute any such file or content. To the extent that you delete a such file or content from the public portions of our site, the license you grant to Imgur pursuant to the preceding sentence will automatically terminate, but will not be revoked with respect to any file or content Imgur has already copied and sublicensed or designated for sublicense. Also, of course, anything you post to a public portion of our site may be used by the public pursuant to the following paragraph even after you delete it.