CORONA was the United States program of photo-reconnaissance satellites that was first launched in 1960 and continued in operations till may 1972. It was the first photo-reconnaissance satellite program in the world. It was also called KH-1 through KH-4 after the camera systems; the KH (for KEYHOLE) designations have continued in later satellites. The current generation of U.S. photo-reconnaissance satellites is probably the KH-12.
The Corona program was signed into effect by President Dwight D. Eisenhower in February 1958 and was the first photo-reconnaissance satellite program any where in the world. The program was designed to gather imagery of the Soviet Union, with an emphasis on the Soviet ballistic missile program. While the U-2 photo-reconnaissance aircraft was indeed taking picture over the USSR, it was understood that there was a limited period of time in which the U-2 would not be challenged by Soviet air defenses. U-2 photography was higher-resolution than that of CORONA, but a U-2 was shot down in May 1960 and overflights stopped.
The Corona program was a joint Defense Department/Central Intelligence Agency program, with the satellites being launched by the United States Air Force. The program was operated under tight security and it wasn't until 1995 that the program was declassified. All images are now available to researchers, as commercial imaging satellites have finer resolution. A 1995 conference, of which a film is downloadable, introduced researchers to the collection. 
There was a distinct organizational split between space operations and interpretation. Launching was under the control of what became the National Reconnaissance Office, while interpretation was in a joint military-CIA operation called the National Photo-Interpretation Center, which became the National Geospatial-Intelligence Agency. Different security compartments were applied to the two, the no-longer-used BYEMAN system for operations and the TALENT-KEYHOLE (TK) for the product.
The first Corona satellite launch occurred on 28 Feb 1959 and the last one on 25 May 1972. During this time period a total of 145 launches took place. On 18 August 1960, a Corona satellite took the first images from space. In total, 2.1 million feet (800,000 images) of film was taken.
Key managers in the project included the CIA Deputy Director of Science and Technology, Albert "Bud" Wheelon, Joseph Charyk in the Air Force, and Richard Bissell of CIA. Charyk and Bissell were the first co-directors of NRO.
The Corona satellites was launched by PGM-17 Thor rockets, modified into space launch vehicles from intermediate range ballistic missiles operated by the U.S.A.F. After launch the satellites were placed in a polar orbit at an attitude of 100 nautical miles (185 km). Once the satellite had taken its pictures the film was ejected from the craft while over the Pacific Ocean where the capsule was snatched up in midair by U.S.A.F. aircraft. The film would then be transported to the facilities where it would be processed and analyzed.
At first image resolution was originally 8 meters (25 feet), with an individual image covering an area of approximately 16 km (10 miles) by 190 km (120 miles). Later improvements in the satellite cameras improved resolution to 2 meters (6 feet).
As were all operational U.S. military imaging satellites until the KH-11, CORONA chemically developed the film in space. It then ejected the developed film to be recovered in midair.