Images stripped from Tag description

Hi,
I wanted to add an image to my tag description like on this post: http://www.theshirtlist.com/store/deez-teez/

When I tried to create a new one the image just disappears when I save the description. Clearly it was working before as you can see it above. Even when I copied the above code exactly and saved it to another tag the image code was stripped.

Any ideas what’s going on?

Thanks.