Fighting form spam is something almost every website owner has to face. If you allow comments on your site you will most likely be a subject of form spam attacks. The most effective and most popular way of fighting form spam is using generated images (captchas) that contain text that user should then retype into an input field. Since there are OCR algorithms that can read images, most of the time captchas contain messy and distorted text.
Here’s an anti-spam solution that relies on pure CSS…