It's a photo of 3 very cute kittens. The source is an attachment to a message at another forum where I am a logged in member. Therefore I can see the photo, but for anybody who isn't a logged in member at that forum, you can't see it. It also causes (or at least used to) this forum to keep trying to load the image. I think that it can also cause problems with loading other images in this topic.
This is the same situation that was at Tangles message here at the Humor topic. Tangle apparently later here linked to the photo from a different source.
ps - another test:
I can see it in preview, but I bet no one else can see it.
Can also see it after posted, but only if I'm logged into my e-mail account where the image is an attachment. Otherwise it's a red box containing "Image Not Found".
MORAL - Don't embed photos that are attachments somewhere. You'll probably be the only person able to see it.