Captcha's that are too hard to read

I really hate web sites that use Captcha's when you need to log-in or fill out a form.  These little blighters can make filling out a form a complete nightmare, almost to the point where you hit the back button before you even go any further.

Captcha's for anyone who hasn't actually come across the term before are those little squiggly images where you need to decipher the text (usually some nonsensical combination of letters) which is hidden in an image and then enter it before submitting the form.

There are so many spammers and bots out there...

I can totally understand the reason behind Captcha's because there are so many spammers and bots out there sending all sorts of rubbish down the line to clog up databases and give webmasters a headache.

These guys ARE the scum of the earth (on the Internet at least!) and in my opinion they ought to be hunted down and... well nasty things should happen to them!

The thing that really annoys me is that so many Captcha's are almost completely unreadable by ME never mind a machine!  The last time I looked I was human so I ought to have a fighting chance at deciphering the code.  I often find myself having to click on a link to request a different image or worse still fill out the whole damn form again!

Some sites don't even provide an audio Captcha's so that visually impaired visitors are effectively excluded from using the page.  How bad is that?

Here's a bit of background info from Wikipedia and Capitcha.net.  Go read up and be amazed, there's actually a lot of interesting information on the Wiki.  I just wish there was an alternative because I personally find them frustrating!