Screenshot by Rafe Needleman/CNET

Modern captchas are effective at keeping bots and algorithms from accessing Web sites made for humans. They also generate collateral damage and keep up to 25 percent of humans out, too, according to Ron Moravek, COO of NuCaptcha. He says he has a better, more flexible technology for filtering humans from bots.

NuCaptcha is a replacement technology for the free, Google-owned ReCaptcha service. There are two major differences between NuCaptcha and ReCaptcha. First, NuCaptcha displays moving text against a moving image. While this makes it harder for computers to discern text from background, it makes it much easier for humans. We use relative motion as additional information that helps us see patterns, not as noise to be processed out. This effective processing gap means that captcha text can be shorter--three characters is enough--and that it's much less painful for humans to read the text and proceed past the challenge. "It can be solved in three seconds," Moravek says.

Second, the NuCaptcha system accepts parameters for the strength of the captcha. Just want a lightweight system to keep out most bots and scrapers? You can get a captcha so simple a one-eyed monkey could pass it. But if you want to add more security, like a system in front of a password reset process, you can turn up the heat. Moravek reminds me that Google's ReCaptcha system is not configurable.

Screenshot by Rafe Needleman/CNET

NuCaptcha is free with default options. There are also advertising-supported versions, and paid options for enterprise clients that include features like behavioral analysis: The captchas get harder if the user's activity before he, she, or it hits the captcha looks bot-like. For example, if forms are getting filled out a super-human speed.

Running an entire business around captchas seems to be a particularly weird game of technological cat and mouse. Computers keep getting faster and better at pattern recognition, and the better they get, the more annoying so far, captchas have gotten too. For now, this motion-based captcha technology puts humans back in the lead. It also gives NuCaptcha a--probably temporary--leg up on Google.