This question already has an answer here:
The Area 51 ads, when you click on Share This, provide a link and an image, as well as the corresponding HTML, to advertise elsewhere. This used to work, but when copypasting the image link (that looks something like this:
http://area51.stackexchange.com/ads/proposal/123456.png) into a per-site community-ads question, you get a "Not from Imgur" error. Can't SE itself be added to the whitelisted image hosts?