CAPTCHAs are used in attempts to prevent automated software from performing actions which degrade the quality of service of a given system, whether due to abuse or resource expenditure. CAPTCHAs can be deployed to protect systems vulnerable to email, such as the webmail services of gmail, hotmail, and yahoomail
Most interactive sites today are run by databases and become quickly
clogged and sluggish when a database table exceeds capabilities the
operating server can handle.A website's is safe using captcha