Do good CAPTCHAs really have to be unfriendly?

Jeff Atwood at the Coding Horrors blog discusses whether CAPTCHAs are dead. This follows a news report that scalpers probably beat the CAPTCHAs at Ticketmaster.

Jeff links to a Chinese site that sells CAPTCHA decoders. The site quotes different prices for breaking different CAPTCHAs. An eBay decoder, for example, is being sold for $4000 and claims 70% accuracy.

What caught my attention were the unbreakable CAPTCHAs in the list. The Yahoo CAPTCHA is listed as unbreakable. That isn’t surprising. Most of us can barely get it right ourselves.

Consider this Yahoo CAPTCHA. Is that a G or a 6? Is that p lower or upper case?

Contrast that with this Google CAPTCHA also listed as unbreakable.

The Google image is clean and legible. Most of us have no difficulty getting it right. Google demonstrates that effective CAPTCHAs don’t have to be unfriendly to users.

I am curious to learn which CAPTCHA libraries generate strong, yet user friendly challenges.

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