As everyone knows, captchas can be a real nightmare. Besides their serious accessibility issues (have you ever clicked the “Hear a set of words”?) they’re a real pain in the ass to enter.

It can be very discouraging to a visitor if they have to re-enter the captcha text every time they make a mistake on the form. So frustrating in fact, that they’re likely to give up after making a couple mistakes.

Here’s an example from the Gmail signup, of how not to do it:

Yesterday, I came across a great way to handle this. When you’re signing up for Twitter and you enter the captcha correctly, but make a mistake on another field (like email address), it removes the captcha which means you don’t have to enter it again. Hoorah!

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I’m not sure if Twitter has A/B tested this screen, but I’d bet a chunk of change that it improves signup rates significantly.

On a side note, if you’re a frontend developer, you’ll enjoy two awesome talks by Britt and Dustin from Twitter:

1. “The Future of Frontend Engineering – Learning from Twitter” by Britt Selvitelle
2. “The Future of JavaScript Design Patterns – Unleashing Full Object-Oriented Capability” by Dustin Diaz

Read more at The Future of Web Apps site.