One of the interesting things about CAPTCHAs is that a true CAPTCHA is win-win: they're designed to be hard problems in AI, so if they're compromised, AI research has moved forward. For example, the obfuscated text recognizer can now be rolled into machine vision systems elsewhere. It's an interesting study in incentives. CAPTCHAs give spammers incentive to do something that at least minorly advances society, while AI researchers have an incentive to build CAPTCHAs that are hard (but not too hard--those you save until the easier ones get cracked).

The image identification thing doesn't quite make it as a CAPTCHA. One of the rules of CAPTCHAs is that the entire thing--source code, data, etc--have to be open source; no security through obscurity allowed. So the problem as posed is trivial. Because the originator must classify all the images in order to verify the correct answer from the user, this is available as part of the source and data. Note that even if the originator cheated and did not make this available, the database had to be small enough to be human-classified in the first place, so it won't be long until every spammer has it classified too. Now, if the program were to alter the image in a way that obfuscates it for computers but so that it is still identifiable to humans, this would be an acceptable method.