When it comes to some U.S. government photos, smiling is frowned upon.

"The subject's expression should be neutral [non-smiling] with both eyes open, and mouth closed," says a rule cited in the rejection of a visa photograph of a tooth-showing person from Cleveland. The U.S. Citizenship and Immigration Services explained that "no expression" is the standard for such photos.

The Clevelander's attorney advised Pittsburgh colleagues last week to warn their clients about new, more stringent specifications for immigration photos.

The no-smile regulation is part of a wider policy that went into effect in August. As of Sept. 1, no three-quarter-angle photos, the old standard for immigration documents, and no smiling faces are permitted.

But most people won't know they're not supposed to smile unless they visit the U.S. State Department's Web site and read the lengthy set of instructions for photographs, including colors permitted for the background, proper lighting, directions for eye height, head orientation, and the necessary "natural expression" with no squinty eyes or flashing teeth.

"A smile with closed jaw is allowed but is not preferred," the instructions add.

Mark Knapp, an immigration attorney with Reed Smith, knew about the change in specified angle but didn't know about the no-teeth rule until notified by his Cleveland colleague, Marin Ritter.

"I have verified that this is indeed the new policy. You can't make this stuff up, honestly," Knapp said in an e-mail.

Why the glum faces at the State Department?

"In terms of getting exact facial kinds of things, that's what gives the most accurate information," said Angela Aggeler, spokeswoman for the Bureau of Consular Affairs, which handles travel-document guidelines.

"Actually, it is because, according to the International Civil Aviation Organization standards, the reason is that [smiling] distorts other facial features, for example your eyes, so you're supposed to have a neutral expression. They have determined that to have the most neutral face is the most desirable standard for any type of identification."

Denis Chagnon, spokesman for the International Civil Aviation Organization at its regional office in Montreal, already had fielded the no-smile question last year, when his organization promulgated the new standards for photos and Canada adapted them.

"Ahh, ahh, yes. Very simple. And it's interesting because it made the headlines here in Canada to the effect that you can't smile in Canada anymore. In May 2003, ICAO issued guidelines on the use of biometric information for machine-readable passports."

The United States and many other countries have had machine-readable passports with bar codes for a number of years, he said, but now they are moving toward a system in which biometric information is to be included, too. A computer chip embedded in the passport would allow a cross check of the person presenting it by using a facial-recognition computer program as well as checks of other biometric information such as fingerprints.

"You go to the airport, there will be a camera at the immigration counter or customs counter, and the system will compare your picture with the picture on the chip [in your passport or immigration document]," Chagnon said.

"To allow for best possible comparison, if you smile or blink your eyes or turn your head, there would be fewer comparison points. So when you go to the counter, you will look at the camera in neutral face to offer the best comparison to the matching points on the picture in the passport."

So if you had people smile broadly, teeth and all, for both the passport photo and at the counter camera, you could still match the two effectively?

"You'd probably have to develop specs for smiling," Chagnon said, laughing, perhaps with teeth showing.

"Local immigration attorneys were bantering it back and forth for a while," Knapp said. "What is interesting is the idea that you can't smile anymore and that they're rejecting photos. The idea that you can't smile is what most immigration lawyers find absurd."

Some firms that take passport and immigration photos said they had received some information about the new specs.

"We got something in the mail," said Tom Campano, owner of Mail Boxes Etc. on Craig Street in Oakland. "I'm looking at the thing. We have the specs on the wall. They go into passport size and dimensions."

His posted information, however, didn't include the no-smile rule, and he was unaware of it.

"Most people don't smile anyway," he said. "I'll have to keep that in mind."

Janet Stewart, of Chircosta Studio on Smithfield Street, Downtown, learned of it the first day it went into effect, by having a photograph rejected. Her business takes many immigration photos, and she now advises everyone not to smile.

"I'm the only photographer that says, 'Don't smile,' " she said.