validation code : Java Glossary

A variant asks you a multiple choice question to identify a picture. This is less stressful than a typing test.

The catch is you can’t tell o from O from 0 in isolation, or i from l from |, etc. I have complained to the creators of these torments and they ignore me. You have a similar but not so serious problem keying serial numbers and Windows activation codes. Any time you want people to key random gibberish, e.g. serial numbers, activation keys and validation codes, the number should not use the characters 0 o O 1 l. Alternatively, you can use the ambiguous letters but treat all similar-looking letters as equivalent. This does not reduce the psychological stress on the person typing however.

CAPTCHA

You will see the technique used on Blogger. Unfortunately, the creators of these tests usually require you to distinguish 1 from l and 0 from O from o without any meaningful contexts. So they waste the user’s time with ambiguous images. It usually takes me about 3 tries before I am able to type the code. Each time I am convinced I have it correct. It is a great way to infuriate your customers.

Though not part of the Captcha, sometimes the box you are supposed to type into is almost invisible like this:

How To Cheat

Recaptcha