Pretty good,
Although, keep in mind OCR/ANNs can read text (ANNs are often trained for text recognition, however object recognition can be much harder due to the wide variation) , so asking the user to describe an image/picture/object rather than text within an image often holds ground for longer (even with the additional logic of the question)
I'm about to upload an add-on to allow admins to create their own captcha's (free), users can then share/sell their captcha sets (so it has import / export functionality too)
Basically it is a "custom image captcha" plug-in, this plug-in and your idea share the advantage of QA's (in that they are often original, and not from a large database of "known images"), and the advantage of some image captcha (it weeds out the basic bots that can not easily read text / solve logic from images)
If users create their own customisations, it's so much harder for bots to solve (as long as they avoid simple text / logic being read from the image that makes it easy to solve)
I'll upload this add-on tomorrow... I'm just testing it now.
An example set that I just created and wanted to give away with the plugin (obviously you will be able to add/delete any image you want to your own set):
Although, after having looked at this set, if the text "animal beginning with S" was stripped out from the image, the bot could then retrieve a brute force list:
The software is also able to gather and decipher artificial intelligence such as security questions (i.e. what is 2+2?) often used by forums upon registration. Since the latest version of XRumer, the software is capable of collecting such security questions from multiple sources and is much more effective in defeating them.
Helper program Hrefer is also included. This software is used to automatically parse results from search engines including Google, Yahoo, Bing and Yandex for forums and blogs that can then be used as a target list for the main XRumer application.[citation needed]
http://en.wikipedia.org/wiki/XRumer
The text is there to often make it more user friendly, but in doing so, you can often reveal too much to the bot.
So this set isn't very good after all. It would be much better if the set was "objects begin with S", the list to brute force this would be much larger making it less likely for a bot to successful register
If a bot can read your text, and can solve your logic, it might be able to register (although, I think many will have trouble with reading the text and solving the logic in combination for now)
Edit: I have now added this resource
http://xenforo.com/community/resources/customimgcaptcha.1161/