PROBLEM

There's been quite a bit of discussion on this subject in recent times, but after browsing through many threads, a definitive solution was not obvious.

Using contact forms on my websites has greatly reduced my email spam, but now the inevitable form spam has started, and is increasing at break-neck speed.

The format they use is always proper for an email, but the emails are never real.

SOLUTION

CAPTCHAs are used to prevent bots from using various types of computing services. Applications include preventing bots from taking part in online polls, registering for free email accounts (which may then be used to send spam), impeding OCR detection of spam in images attached to email messages, and preventing bot-generated spam by requiring that the (unrecognized) sender pass a CAPTCHA test before the email message is delivered. They have also been used to prevent people from using bots to assist with massive downloading of content from multimedia websites. CAPTCHAs are used in online message boards and blog comments to prevent bots from posting spam links as a comment or message.

CAPTCHAs are by definition fully automated, requiring little human maintenance or intervention in administering the test. This has obvious benefits in cost and reliability.

The algorithm used to create the CAPTCHA is often made public, though it may be covered by a patent. This is done to demonstrate that breaking it requires the solution to a difficult problem in the field of artificial intelligence (AI) rather than just the discovery of the (secret) algorithm, which could be obtained through reverse engineering or other means.

Sample the Application