I once read in WIRED about a scheme related to this, in which humans were augmenting the fake account process. The situation they described involved a spam program that would sign up for accounts on chat servers that had such distorted-text verification schemes (or other schemes, where a user might identify the object in an image) by sending the image to humans whose only job was to identify its content. WIRED reported that these people were often teenagers getting access to pornography in exchange. But it doesn't sound exactly like something that'd happen in real life or scale comfortably.

It seems like the identification of what object an image is depicting where the number of possible images is very large might also be a good verification method. There are large databases of stock photography images on the internet as I'm sure you're aware. Imagine being asked to identify the animal pictured, and there are 10,000 different photos of dogs that could be displayed which are, to humans, obviously all dogs. The problem with this method is while it makes it much harder for a computer to identify the image, it could severely limit the number of ways an image can be identified.

But in the world of weblogs, this could be a real cute way to verify the human-ness of a poster if you weren't so worried about it being very strong, as maybe you could pick your own images (am I happy or sad in this picture?) or something.