CAPTCHA is a inevitable thing for each site. I didnt understand why i should pass the CAPTCHA before posting something or doing something on internet. Until I read this artical and get a further understanding.The purpose is distinguishing between machine and people. but as the Chad perrin said , it is not really good one. I don’t believe images generated by a computer program cannot be identified by a computer program.There is no 100% safe CAPTCHA. sometimes I registered some services online, the CAPTCHA is too difficult to see, I have to refresh many times to identify it. It is very troublesome.
There are some better ways in this article. one of them is”trackback and pingback source checking. Chad Perrin gives a example to explans how it work . that is someone sets up a blog with that accepts trackback and pingback. and you also sets up weblog with this functionality. when you want to post something intresting about someones blog post, you just post on your own blog ,with a link to others post .The pingback and trackback sent notification,and the other site tucks a reference to your post into its comment stream or special trackback section. the two blog will be automatically link to each other.by setting up trackback and pingback ,you can ensure that those things will be rejected outright without having to lay eyes on them yourself.