The code is known as CAPTCHA (sample below). A CAPTCHA  is a type of challenge-response test used in computing to determine whether the user is human. Before the release of this newly designed web site, our guest books would receive hundreds of SPAM/Junk that were being posted by automated means. Although steps were taken to eliminate the problem they were only partially effective.  The task of maintaining and removing the SPAM/Junk from the guest book was becoming time consuming.  CAPTCHA was also put into place on our Young Marine web site and the SPAM/Junk has been reduced by 100%. To learn more about CAPTCHA,  please visit Wikipedia Encyclopedia.