And when you smile for the camera
I know they're gonna love it

--"Peg" from the Steely Dan album "Aja"

In a way, this 1977 lyric sums up Americans' recent attitude toward family photos. From the Jumbotrons in baseball parks to the Facebook and YouTube Web sites, we grin and wave at the camcorder, the cell phone, the instantaneous images of our digital age.

Initially, the conventions of family photos were earnest, but changed after photographic technology improved, ushering in the point-and-shoot era of instamatics and Polaroids.

"[Andy] Warhol always said he only was interested in the record, not the process of photography. He only used the original point-and-shoot Polaroid," said Tom Sokolowski, director of The Andy Warhol Museum.

In the 19th century, making photographic portraits was far more complicated and time-consuming.

"People did not smile when they were photographed,'' said Linda Benedict-Jones, who teaches the history of photography at Carnegie Mellon University and is executive director of the South Side's Silver Eye Gallery. "Having your likeness made was such serious business. Your parents were paying a lot of money."

The exposure time needed just to make one photograph was much longer, too.

"The first photograph had an eight-hour exposure. Then, as technology improved, exposures were two minutes, 1 minute, 30 seconds," Ms. Benedict-Jones said. So holding a smile for 30 seconds or two minutes was difficult.

In 1871, Edward L. Wilson, a Philadelphia photographer, distributed a pamphlet that outlined how to pose children.

"Never threaten a child if it won't sit, and never coax it with sweet-meats. ... Dress the little ones with care and good taste. ... A sitting or kneeling attitude is best, for few little ones stand quietly long enough to have a picture taken."

The Carnegie Museum of Art's "Picturing Childhood" exhibition shows how George Eastman's invention of the Kodak camera in 1888 made photography available to the masses. The exposure time in that era may have been one second, Ms. Benedict-Jones said.

"In the 20th century, lenses get faster and sharper. Cameras get smaller and more portable and the film gets faster as well. And so, everything becomes easier," Ms. Benedict-Jones said.

Small children may still fidget in front of a camera, but today the exposure time for making a picture may be 125th of a second.

The images that teenagers take of themselves and post on Web sites like MySpace and Facebook are "visual sound bytes. It's so ephemeral, so erasable. You can make 100 pictures and you only print 10 of them," Ms. Benedict-Jones said. Unlike the "Picturing Childhood" photos, they're not what photographers call "decisive moments."

When her two sons were young, Ms. Benedict Jones said, she photographed them frequently, then stopped, reasoning that participating in her children's lives was more important than recording them.

Paul Friday, chief of clinical psychology at UPMC Shadyside, said that was a wise move.

"The difference is between capturing now or living it. You have to figure out if you are going to be a participant or if you're going to be the historian."

Parents or teenagers who take pictures constantly should practice some moderation, Dr. Friday said.

"Our sense of self can be altered if we're constantly seeing our own images. It's almost like creating a narcissistic society. Narcissus died not because he fell in love with himself. He fell in love with his image. A lot of people think -- incorrectly -- that narcissism is loving yourself. It is not. It is loving your image.

"What happens to these images? They go away. They're gone. It's like those trays upon trays of slides. Our generation has stacks of them. No one ever looks at them. Our parents had boxes and boxes of pictures that were never organized. Now what we have are the people who have deck upon deck upon deck of VHS tapes of their children playing ball."

Ultimately, Dr. Friday said, "We all need private lives that are not on film."

Julie Saul, owner of Julie Saul Gallery in lower Manhattan, specializes in exhibiting photographs. The widespread use of cameras, she said, led to the democratization of visual culture.

The ease with which cell phones capture pictures, Ms. Saul said, can make the act of making images "sort of meaningless. The easier something is to do, the less meaningful it is, I think. The nature of it changes. It's less formal.

"In high school, we took those gorgeous black and white formal portraits. You wore a nice dress with a scoop neck and had your hair done."

While she cannot predict what camera technology will look like 20 years from now, Ms. Saul said the impulse to share images on Web sites and digitally will continue.

"Unless people are really disciplined, we may have less of a material record than we have had for the past 100 years," Ms. Saul said. "Right now, I'm not absolutely sure that people have gotten to the bottom of how digital imagery is safely stored in perpetuity."

Ms. Benedict-Jones agrees. Twenty years ago, she urged her students to shoot at least one roll of family photos each year with black and white film. Now, she reminds them to print their photographs.

"The prints in the Carnegie Museum of Art show were made 120 years ago. In five years, where will digital images and prints be? Color fades. Black and white lasts."