How does this hassle users more than regular captchas? The only additional effort it adds is a bit of thinking (too much to ask these days?). You don't have to type anything and it replaces the "Submit" button so not even any extra clicks.
It's different. I don't think it's particularly better or worse overall.
It suffers from the same issues of forcing commentators to stop and think about something utterly unrelated to the comment they are trying to make, and of being easily defeated by third world workers paid a pittance or first world porn addicts.