Why do you have to answer questions like: "Math Question: What is 1 + 9?" when posting comments?

This is called Captcha and was done to protect our website against SPAM. This is only for anonymous visitors currently. Please register if you post ofthen and Captcha bothers you...

Update:
Currently I've changed Captcha to display image of five letters instead of Math question. The image CAPTCHA is a popular challenge where a random textual code is obfuscated in an image. The image is generated on the fly for each request and displayed below the comments form. 

Please copy the characters (respecting upper/lower case) from the image displayed in the Captcha form.