The biggest issue with audio CAPTCHA is actually the same as with the visual version: just as it’s often hard to see which individual letters are being used, it’s hard to distinguish individual sounds.
One of the problems with audio CAPTCHA that I’ve found is similar to the visual CAPTCHA: there’s so much noise behind the words that are being spoken you can’t identify what they are, Hawkins said.
That noise is added to block automated recognition systems, but in this case the cure seems worse than the problem.
I pride myself on being a pretty good listener, Hawkins said.
Because I’m blind I need to use my hearing in different ways and I find even with that very acute hearing that these audio CAPTCHAs are really difficult to understand.
A secondary problem is that audio CAPTCHAs often use numbers, but doesn’t distinguish them, so it’s impossible to know if you have to type
The solution, as we said yesterday, is to ditch CAPTCHA altogether. Sending a verification email is one solution, though that adds an extra step. Another good alternative is asking site users to solve a simple maths problem — an option that works well with screen readers, Hawkins said — via Lifehacker Australia