How Long Imgur Stores Uploaded Images

I can't actually find it documented anywhere, but I uploaded an image and played with the "More Sizes" list:

Original

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.

Large thumbnail

http://i.stack.imgur.com/YdJZtl.jpg (added an l after the image ID)

Small square

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.}

You need to get into the gallery to get captions. How do you do that?

To get your image into the Gallery, it must be spread all over the Internet and gain a certain level of popularity. This means that you’re still able to upload images and have them remain private (just don’t share them all over the Internet!) while still being able to view the best images out there.

Source: http://imgur.com/faq#gallery