CAPTCHA (Completely Automated Public Turing Test to Tell Computers and Humans Apart) is a test to ensure that response is generated by Human, rather then an automated computer. This is developed by Carnegie Mellon University and being implemented by number of online clients.
Yahoo uses Captcha to eliminate bots from entering Chat, but this has been cracked by Russian Hackers.
Rapidshare.com introduced a new form of Captcha which is more human readable then the previous method which involved entering four character with a cat ( cats and dogs have similar heads ). Rapidshare suggested tip for figuring out:
“The sitting animal is the cat.
The standing animal is the dog.”
One way to avoid Captcha is to wait until Rapidshare Happy Hours are active where downloads can be made without entering Captcha. Rapidshare Happy Hours are active between 0:00 – 18:00 UTC+1 on Mondays to Fridays and 0:00 – 14:00 UTC+1 on Saturdays and Sundays. Easy way is to install the firefox add-on Happy Checker which reminds when the Happy hour is active.
If your looking for best Rapidshare search engine, read this post. A lot of people have been uploading movies, music, applications, documents into rapidshare. It has become a popular source for warez.