Nobody knows you're a dog on the Web--or a mechanic, athlete, hacker, marketing whiz, zealot, or SQL programmer. That is, unless you tell them. In which case, they may or may not believe you, and they have few options for verifying your credentials anyway.

It's hard enough to know who's who in the physical world, where you can look into a person's eyes and, if necessary, ask to see a driver's license. The Web's built-in anonymity makes identification harder, authentication a science, and accountability nearly impossible.

Does it matter? Wikipedia thrives as an encyclopedia by the people. Digg volunteers determine what's news. Some Facebook users trust one another enough to share phone numbers. Even China backed away from plans to force bloggers to use their real names.

Make no mistake, though; online identities matter, and they'll matter even more as the number of blogs, wikis, and social networks grows, making it increasingly difficult to sort out the Web's wheat from the chaff of misinformation, factual errors, and malware. What we need--bloggers, businesspeople, technology professionals--are better ways to let others know who we are, verifying what we tell them and showing that we've got the cred to back it up.

Such a system would let online shoppers know more about sellers, and content consumers know more about content creators. As more organizations adapt Web 2.0 technologies and principles to conduct business, digital identities will help their employees establish their own credentials while telling them more about their customers.

Sanger: Credentials only, please

"The idea of a transferable, semantic reputation is identity nirvana," says Fred Stutzman, co-founder of ClaimID, one of the many startups trying to help Web users create more complete and flexible online profiles.

Web identity systems exist in many forms, from Microsoft's Windows CardSpace identity manager to LinkedIn's way of letting users recommend one another based on previous experiences. But they're mostly narrow in scope and not foolproof. "When are we going to have certs that are better than self-assertions that I am a great guy, I am who I say I am, and I say you can trust me?" asks analyst Michael Cherry, with Directions On Microsoft.

Wikipedia, the community-generated online encyclopedia, has had its reputation damaged by "experts" who didn't live up to their billing and by postings that proved to be inaccurate. In one notorious example, journalist John Seigenthaler Sr.'s Wikipedia profile was vandalized with misinformation that suggested he was involved in the assassination of John F. Kennedy.

Processes in place at Wikipedia are meant to prevent such gaffes. At their discretion, site administrators can protect articles from changes or even ban users. But that works only when the admins themselves are trustworthy: One administrator who went by the pseudonym Essjay claimed to be a tenured professor in religion but turned out to be a 24-year-old community college dropout.