A non-graphical CSS CAPTCHA

[ExplainThat]

A technique for creating a non-graphical CAPTCHA using CSS alone is described here.

The technique relies on the fact that HTML element borders can be individually styled using CSS and makes use of the CSS float attribute.

The technique is presented largely as an interesting demonstration of what can be accomplished using CSS. The CAPTCHA in its current form could be solved programmatically with no great difficulty. It is possible to create a similar CAPTCHA that would be a great deal harder to crack but I am not sure it is worth the effort.

In any case, I am curious to have some feedback and - should anyone care - see any attempts at writing code to solve it.

[Twey]

As an academic exercise this is interesting, and I'd be happy to provide feedback and code. It doesn't provide any significant advantage over an image-based CAPTCHA, however, and the code required is, as you say, much (much much) more complex, especially if you're intending to make it difficult to break.

[ExplainThat]

Purely an academic exercise really - just wanted to show a neat way of using CSS. I don't seriously expect people to start using this as a CAPTCHA.