Anonymity No More? Age Checks Come to the Web.

Some services are resisting the checks. Twitter allows users to disclose their birth date but does not require it. If users want to view adult content — nudity is prevalent on the service — they must click through a warning but don’t have to prove they are 18 or older.

“At the heart of Twitter is the belief that there’s a huge value to the public conversation of people being able to speak pseudonymously to the world,” said Nick Pickles, a senior director of global public policy strategy at Twitter, “and also not requiring a significant amount of personal information to be provided before you can use online services.”

The shift might be especially troublesome for some people, critics said. Posts related to lesbian, gay, bisexual and transgender people are more likely to be mistakenly marked as “adult” content even if they are not overtly sexual, for example, said Ms. Barnett of the Electronic Frontier Foundation.

Automatic facial analysis is also often less accurate for female faces or people with darker skin. And critics worry that strict age checks could make life more difficult for people who rely on anonymity online, like sex workers and political dissidents.

Perhaps no part of the web has more new age check requirements than pornography sites, which are often at the leading edge of technology trends. In addition to Germany and France, governments including Poland, the Philippines and Canada have considered proposals that would require pornography sites to check ages.

“The internet was created by adults, for adults,” said Julie Inman Grant, who runs Australia’s Office of the eSafety Commissioner and has been developing age-check guidelines. “And I think one of the key challenges for us is to come up with a system that proves a child is a child sitting behind a keyboard.”

It is unclear how internet users will respond to the increasingly common age checks.

For months, YouTube explained to frustrated users on Twitter that it was demanding government IDs because of new regulations.

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