It's ok effective judging by my usages and I could just iterate over this solution if someone brute forced it or implemented a "cat fur detector" (which for my uses is pretty unrealistic).

Battling spammers is really a battle where you implement better protections and they implement better attacks. The conclusion so far has been that it isn't possible to check-mate them - - and it's very unlikely it will ever happen as a lot of spammers use "human bots"...

Using visual captcha is much more user friendly thought, so it's a win for the users.