[Darkphibre]

I suppose the argument would be that the key search space is reduced. Statistically speaking, you know the weights of certain binary pairs if the image is not evenly distributed. But I'm guessing that it'd only drop the average search space by... two or three powers of two for most keys?

[duskwuff]

Again: the randomart image is based on a hash of the public key. If you want to know what that key is, all you have to do is ask the server. You don't need to launch a sophisticated, expensive cryptographic attack to obtain it.