I am currently working in asp.net, I m all new to web programming. I have to make a website for our clients, we will give them a user id and password of thier equipment and the details (given by the clients) will be entered in the database.

My questions is that, when we create an account in , say yahoo etc, then they show an image with moving or tilted characters for verification. What is the purpose of that images?? and how do they verify the account??

Captcha Image(image with moving or tilted characters) Verification is a method of preventing automated bots (or Scripts) from gaining aaccess to web page features, tyically submission forms. An image is presented for the user, with a number of characters. As part of the form completion the user enters the characters shown in the image for verification. The expectation is that automated robots are less able at distinguishing the characters than the human eye. Captcha Image verification ensures that the user is indeed a human and not an automated robot of script.
How it works?
- We generate a random string and place it on a temporary image
- We show that image in the form
- We make a hash out of that string and send it as a hidden field of the form or we use sessions or cookies to store it.
- When user submits the form the text he entered is hashed and compared with the original hash. If they are equal then user entered correct captcha text.

Thank you :)
Nice piece of information
Now i can use it in my website :)
Thanks alot

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