‘Human Input Validation’ (also know as CAPTCHA) not only harms usability, but breaks anti-discrimination laws in many countries. In addition, recently spammers have begun to use tactics that defeat the process (as reported by the BBC in the article PC stripper helps spam to spread).
Many websites using forms now show an image of some text which the visitor must enter into a textfield to proceed. The purpose of this is to stop automatic form submission by computer programs, which may be malicious.
It is not just computers that find the text difficult to read — visitors with visual impairment will also be unable to fill in the form. This is not only inconsiderate; if the form is on a business website, this is illegal in many countries (for example, in the UK it would be illegal under the Disability Discrimination Act 1995).
For more information on the use of forms, and other usability issues, try Jakob Nielsen’s excellent book, Designing Web Usability:
- Designing Web Usability at Amazon.com
- Designing Web Usability at Amazon.co.uk (for British readers)