In the past, people put pictures they didn't like in the closet. Nowadays, they are advised to put their best photos there. Exposure to humidity, pollution and, especially, light is seen by conservators to drastically shorten the lives of photographic prints and negatives.

But keeping one's collection hidden is no answer, and few collectors or takers of photographs who live in warm or polluted climates would choose to move to make their pictures happy.

There has been a certain amount of noise in the relatively new field of photographic conservation, and some conflicting ideas on what to do.

"Photographs fall apart quicker than people can come up with ideas about how to save them," says Grant Romer, head conservator at the George Eastman House in Rochester, N.Y. "The main problem is people. They don't know what to do and, invariably, they do the wrong thing."

Photography conservation became an area of concern back in the 1970s, when the prices for pictures began to skyrocket. "People have only treated photography as a fine art over the last 10 years, and conservation efforts are only that old," said Douglas Severinson, a photography conservator at the Chicago Art Institute.

Most photographs are simply paper with a thin chemical coating, and they can be easily damaged by the environment or just rough handling. Too much direct sunlight and high humidity can activiate that chemistry, causing fading and discoloration, or they may warp the paper and lead to the image flaking off. Fingerprints are just as bad, as they contain oils, salts and amino acids that may damage both the paper and the image.

According to most conservators, the optimal relative humidity for black-and-white prints is below 50 percent. Photographs stored in humidity of 70 percent or more, such as in an attic or basement, may grow mold (which lives on the gelatin emulsion -- the layer where the image is formed) or become brittle. Fluctuating humidity is the worst thing for prints, since both the paper and emulsion expand and contract in different humidities, but not at the same rate. The bonding between the paper and the emulsion then may be damaged, leading to flaking.

Most 20th-century black-and-white photographs, if protected and handled with care, are relatively permanent. Color prints are a bigger question mark. No one is certain how long they can last without fading or discoloring, though most conservators believe they will show changes within 10 to 20 years, whether they are displayed or not.

The silver compounds in black-and-white prints are inorganic and do not deteriorate significantly when exposed to a moderate amount of light (and not at all when kept in darkness). Color dyes, though, are organic and very susceptible to fading both in light and in the dark.

With both Kodak and Polaroid, the colors change and fade the least when kept in a refrigerated vault. "There is a geometric increase in a color photograph's life expectancy as you reduce the temperature," Severinson says. "Going from 75 degrees F to 60 degrees F, a print's life expectancy can be tripled. From 75 degrees F to 40 degrees F, it can be increased 20 or 30 times. It's just a basic concept that, as you reduce the temperature, you slow down the chemical reactions that cause the deterioration."

One cannot, however, simply put color prints or negatives into a normal home refrigerator because of the higher humidity levels which, in conjunction with the cold, would cause the photographic material to rupture, embrittling the paper and leading to severe flaking. It is possible, however, to prevent some deterioration simply by having an air-conditioner or a dehumidifier in rooms where prints are displayed or stored.

One of the reasons for color photography's inherent problems is that both Kodak and Polaroid color films were not designed for longevity. "They were intended to be inexpensive and easy to process in high-volume, drugstore printing," a spokesman for Kodak explains.

Light, which creates a photograph, also may destroy it -- and so may a variety of other environmental factors. Whether the photograph is a $20,000 Ansel Adams or just a favorite snapshot from a vacation, proper care is essential. Closeting a work is contrary to the reasons for having it, but so is neglect.