This is only happening on CH with avatars - everyone's avatars. They appear for a split second and then disappear.
On my profile if I go to edit it, I can view my avatar next to the radio box marked "I will upload my own picture" but nowhere else at all.
The mini profiles next to the posts are collapsed around the missing avatar, I don't see an "image missing" box or anything.
I can see other images here for example signatures, attachments, the image of my avatar in the previous post.
Some other web pages do in fact have missing images too but this is at random. The only one that comes to mind isn't a site I'd post here as it is illegal, but it's purely for research purposes, not for my own use. There however the image is missing but the site is not collapsed around it, presumably because of the height and width attributes. I do see the image on this site if I right click where it should be, copy the location, and paste into my address bar.