ASP.NET 3.5 and above only
Obout.Ajax.UI Controls - Captcha. Free for all.
The obout Captcha controls allow you to ensure that the form's response is generated by a person.
The CaptchaImage control generates images with distorted text that can easily be read by a human, but does not allow different robots to read the text.
The CaptchaValidator control allows you to integrate the CAPTCHA technology with the ASP.NET Validation.
The obout Captcha controls support all major browsers: Internet Explorer, Firefox, Opera, Safari and Google Chrome.
Unlike similar controls of other manufacturers you can easily combine CaptchaImage
and CaptchaValidator with any TextBox controls.
You can easily create a user control with the look you want.
The distortion is easily controlled
You can control the background color and noise, the width, height and the line noise of the image.
The level of the text's distortion is also controlled.
All this is done with the corresponding properties of the CaptchaImage control.