Spamming is one of the big headaches to the web masters. Spammers abuse their electronic messaging system; post messages on blog, forum or guest book, or send spam emails to get free advertisement. This issue becomes more serious when they use automated spam program or robot for spamming. So in all modern scripts available today have inbuilt spam blocker system. Below, I shall discuss some commonly adopted anti spam system used by the web masters in blocking spam.
Captcha image verification method is the most popular method to block spamming. In this method an image of text string is displayed over the form to be submitted. Users trying to submit messages have to type that image verification text on a textbox to pass through that process. Human beings can easily read that text from its image but for an automated spam program it is almost impossible to extract text unless it uses good quality OCR (optical character reader) software. With deliberate addition of some noise and distortion over the Captcha image makes it even harder to read. Advantages of Captcha image verification are,
The disadvantages are,
In this method a random but simple question is displayed over the form; user has to type the correct answer to pass through this process. Example of such questions are, "fire is hot or cold", "type color of blood", "add nine with seven", etc. The advantages of this method of spam blocking are,
The disadvantage is that it provides very low degree of protection against spamming compare to Captcha image verification method.
You can't prevent spam by banning few email or IP addresses. This method only gives you some extra level of security. Few webmasters ban a group of IPs from where most spam messages are coming. In such sites if you try to register to post your comments you first experience a ban notice over your IP and request a message to contact to the webmaster to overcome that problem. So this spam filter method filter out the spammers and the good users as well.
Whatever the method used the ultimate goal of all such methods is to provide high degree of protection to the robots without harassing the general users. So when you are selecting a spam protection system careful about the following points.