A CAPTCHA is a program that can generate and grade tests that humans can pass but current computer programs cannot. For example, humans can read distorted text as the one shown below, but current computer programs can't:
Guidelines
If your website needs protection from abuse, it is recommended that you use a CAPTCHA. There are many CAPTCHA implementations, some better than others. The following guidelines are strongly recommended for any CAPTCHA
- Accessibility.
- Image Security.
- Script Security.
- Security Even After Wide-Spread Adoption.
reCAPTCHA | http://www.google.com/recaptcha
reCAPTCHA is a free CAPTCHA service that helps to digitize books, newspapers and old time radio shows. Check out our paper in Science about it (or read more below).
Capthas.net | http://captchas.net/
A CAPTCHA image shows a random string which the user has to type to submit a form. This is a simple problem for (seeing) humans, but a very hard problem for computers which have to use character recognition, especially, because the displayed string is alienated in a way, which makes it very hard for a computer to decode.
ProtectWebForm | http://www.protectwebform.com/
Insure yourself from spam! The Anti Spam Insurance Company - ProtectWebForm!
Spam is not delivered manually. There are many so-called spam robots (bots) which are spidering the web in order to find the form. Whenever such robots find the web form it tries to post a spam message to it. The only solution to protect your form is to add a verification image. This method will not protect you from spammers that are delivering their spam manually, but it will stop all the spam bots. Statistics show that spam delivered manually is less than 0.01% of all web form spam.
Classic ASP Security Image Generator (CAPTCHA) http://www.tipstricks.org/
Generate images with letters and numbers to make a CAPTCHA test.
- Completely FREE Classic ASP VBScript.
- The secure code is completely random.
- Dynamic image processing.
- No image file requires.
- No components require.
- Create a cross browser compatible BMP images.
- You can use a custom color palette for image.
