[[Explain what it is.]]

A link to the comprehensive Wikipedia definition: [http://en.wikipedia.org/wiki/Captcha].

[[Summarize highlights of 
http://groups.google.com/group/comp.lang.tcl/browse_frm/thread/622443c5610dda34]]

[[Make more references from http://wiki.tcl.tk/_search?S=captcha%2A]]
----
[Category Glossary]