It's odd; I use Sync Ultra, and while sometimes it uploads images for posts and comments just fine, at other times it simply refuses, and there doesn't seem to be a pattern to the failures or successes, so I've fallen back to Imgur during those times.

Here's a great example! Just tried to upload this copy. First try, it didn't upload and didn't even produce an error message. Second try, uploaded no trouble at all. It's bizarre.