FYI: The access code image and entry requirement you see above and on more and more online forms across the Web is called a "CAPTCHA."
A CAPTCHA (an acronym for
"completely automated public
Turing test to tell
computers and humans apart", trademarked by Carnegie Mellon University)
is a type of challenge-response
test used in computing to determine whether or not
the user is human. The term was coined in 2000 by Luis von Ahn, Manuel Blum,
and Nicholas J. Hopper
of Carnegie Mellon University, and
John Langford of IBM.
A common type of CAPTCHA requires that the user type the letters of a distorted image, sometimes with the addition of an
obscured sequence of letters or digits that appears on the screen. Because the test is administered by a computer, in contrast
to the standard Turing test that is administered by a human, a CAPTCHA is sometimes described as a
reverse Turing test.
CAPTCHAs are used to prevent bots from using various types of computing services.
Applications include preventing bots from taking part in online polls, registering for free
email accounts (which may then be used to send
spam), and, more recently, preventing bot-generated spam by requiring
that the (unrecognized) sender pass a CAPTCHA test before the email message is delivered.
Source: "CAPTCHA," From Wikipedia, the free encyclopedia