Abstract: The problem we solve with this system is the spam on website's forms. Until now this problem has been solved with CAPTHCHAs that help to distinguish between the human users and spambots [0003]. The CAPTHCHAs approach is not a good solution because it does not prevent spambots to read and understand the content of CAPTCHAs. So web sites have to use more and more difficult CAPTCHAs, but human users can't read and understand them. The system, that is described here, provide a solution completely different to avoid spam on web's forms without annoying the human users. The spread of smart-phones increase the needs of an automatic anti spambot filter. When a web site receive a form compilation request ask to the system if it is a human user or a robot. The system check it without requiring the user to do anything. The system can work underneath the web page or it can publish an image on the web page. This image can be an advertising message.