The anti-spam thing is HORRIBLY BROKEN.
I just wasted ten minutes of my life trying to register for this forum; I can only imagine how many users were dissuaded from completing registration due to issues similar to what I faced.
Basically, the anti-spam question loves to report
The submitted form was invalid. Try submitting again.
You have provided an invalid answer to the question.
"What LXDE utility can configure your desktop theme?" -> LXAppearance -> "You have provided an invalid answer to the question."
"What is the display manager in LXDE which gives you login window?" -> LXDM -> "You have provided an invalid answer to the question."
"What LXDE utility can set your screen resolution and rotation?" -> LXRandr -> "You have provided an invalid answer to the question."
"What is the music player used in LXDE?" -> LXMusic -> "You have provided an invalid answer to the question."
"What is the session manager used in LXDE?" -> LXSession -> "You have provided an invalid answer to the question."
"What is the image viewer used in LXDE?" -> GPicView -> "Your account has been created."
If these are indeed NOT the answers then you need to re-think your questions, because after Googling the first one or two I consulted your very wiki for the answers and still got rejected. I think I even got the image viewer question earlier in my registration quest, and it rejected that very same answer... so chances are, something's broken with the plugin.
I say stick with what works, and use a vanilla reCAPTCHA plugin. Sure, sometimes it comes up with illegible text, but usually a refresh or two gets a decipherable image and the user can move on with registration.