Demo of Javascript Captcha
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Javascript CAPTCHA

CAPTCHA is the name for those safety measures designed to prevent robots from repeatedly attempting to log into a website. Usually they take the form of an image that is shown to the user. The user then has to type some letters into a form.

This is a form of "captcha" that is driven by a Closure-Style Javascript Class. It is totally encapsulated, with three publicly accessible methods:

It is instantiated after the page loads in order to draw the keyboard, and set up the handlers:
document.getElementById("keyboard").innerHTML = oKeyboard.getKeyboardHTML();

What it does is deliver a keyboard where each row of keys is randomly scrambled. The user has to have human intelligence in order to input his data.

You can try by inserting data, and then submit the form. A server script will show your input. You can also redraw the keyboard to watch its random arrangement.