subject: Captcha An Effective Technique To Fight Automated Submissions [print this page] Our days have computers and the Internet, to fill to the point where software can run tools (such as standalone programs or web scripts) automated tasks on the Web, such as browsing a website (spiders) and send Web forms developed.
This task was difficult, a few years ago, and people have not thought much about it at the time. But now, complete with the increasing amount of spam, and advanced scripting languages, many hackers and spammers in writing and using scripts and submit forms automatically.
Many sites (all major ones) are a means to automate that are growing in popularity: CAPTCHA to block further.
A CAPTCHA (an acronym for "completely automated public Turing test Computers and Humans Apart Tell, protected from Carnegie Mellon University) is a type of challenge-response test to use in computing, whether the user is human.
A common type of CAPTCHA requires that the user points a distorted image, sometimes with the addition of an obscured sequence of letters or digits that appears on the screen. This rule ensures that only man can give the right answer, because it is difficult (but not impossible!) For machines to extract the letters and numbers on the screen.
CAPTCHAs are common expecially on web forms where the user is in the process, a kind of information as a URL, a comment, office, or for certain services that prevent, register using automated software actions such as posting to blogs or Forums lead, creating a large number of unwanted memories automatic notifications.
CAPTCHAs are by definition fully automated and requires little maintenance or human intervention in the administration of the test. This has some obvious advantages of cost and reliability.
How CAPTCHA Works.
The website has a new CAPTCHA unique every time the page containing the web form will generate visits, has included this picture not letters and numbers in every part of the HTML page. A common mistake of Captchas is to contain code to be displayed in the filename of the image (eg [http://www.myserver.com/captcha-SAQSK0.gif], where the code is that SAQSKO must be entered by the visitors).
Captcha images are from a script (are usually PHP) generates selects a random string of letters and numbers, one police at random (see among many), and some noise on the image and then creates a new image with them.
