Blogs can be plagued by spam comments. They’re created by a type of automated script that finds new blogs and sends a “comment” for approval. People send massive amounts of them, hoping you’ll approve their comments. Your approval automatically creates link to their sites and increases their visibility.
A CAPTCHA script requires your visitor to type a few letters into a text field before hitting “submit”. This simple human-versus-computer process completely eliminates automated spam, because spam software can’t read or type. Only a real person can read and type in the code into the box.
Hacking CAPTCHA codes has become big business in many third-world counties. Read more about CAPTCHA-solving sweatshops and how they work