Since authimage is giving me so much trouble (>2 hours): not showing image, ever since the reload of the server, I have decided to go with reCaptcha. I don't generally prefer services that need a live connection/account creation to different hosts, but after seeing the features and how easy the installation, I'm sticking with this one.
Now, those spammers from China (or using proxies from China) will have an even harder time trying to comment spams on my website.