[Php randomly generated verification code]-php Tutorial

[Php randomly generated verification code]

@ Header ("Last-Modified :". gmdate ("D, d m y h: I: s "). "GMT"); // indicates the last modification time of the content @ header ("Expires: Mon, 26 Jul 1997 05:00:00 GMT "); // content expiration time @ header ("Cache-Control: no-cache, must-revalidate"); // force not to cache @ header ("Pragma: no-Cache "); // disable this page from being cached

In general, the browser will save the pages that have been visited. during the second visit, the cache will be extracted directly, and no further request is required to the server.

In this case, you must ensure that the verification code is different each time, so you must force the browser to request the server each time.

CAPTCHA is short for "Completely automatic Public Turing test to tell Computers and Humans Apart" (a Completely Automated Turing test that distinguishes Computers from Humans, it is a fully-automated public program that distinguishes a user from a computer or a person.