Juxtaposition

There have been some sites where I've suffered the same fate.  Do they want me to match case?  What the heck does the captcha say?

From the NYTimes article a great quote:

“You can make a captcha absolutely undefeatable by computers, but at some point, you are turning this from a human reading test into an intelligence test and an acuity test,” said Michael Barrett, the chief information security officer at PayPal, a division of eBay. “We are clearly at the point where captchas have hit diminishing returns.”

Talking Points Memo: by Joshua Micah Marshall June 11, 2007 10:54 PM

Of late, I've had several captcha fill-ins I was asked to type in where I actually had a difficult time figuring out what the letters were. And I'm human. Really.

To make matters worse, researchers (university ones, not independent hackers) are devising ever-clever ways of beating the tools.

It all depends on your threat model just how obscure you need your captchas to counter the threat but beware captcha's days are likely numbered.