Government agencies have tried to remove sensitive information, only to discover that copies have proliferated and they're virtually impossible to eradicate.

In the not-so-distant past, satellite imagery was restricted to United States government use. Now it's fair game for anyone: News media and individuals may purchase low-cost commercial satellite images. But many fear that, to guard what it views as sensitive information, the government will begin to exercise "shutter control."

Transcript of a Lehrer News Hour background on the U.S. policy of censoring satellite imagery or "shutter control".