On February 29, 1964, President Lyndon B. Johnson announced the existence of the program to the world, but it was done with a certain amount of subterfuge. He said, "The United States has successfully developed an advanced experimental jet aircraft, the A-11, which has been tested in sustained flight at more than 2,000 miles per hour and at altitudes in excess of 70,000 feet. The performance of the A-11 far exceeds that of any other aircraft in the world today. The development of this aircraft has been made possible by major advances in aircraft technology of great significance for both military and commercial applications. Several A-11 aircraft are now being flight tested at Edwards Air Force Base in California. The existence of this program is being disclosed today to permit the orderly exploitation of this advanced technology in our military and commercial program." Later in his remarks, Johnson said, "the A-11 aircraft now at Edwards Air Force Base are undergoing extensive tests to determine their capabilities as long- range interceptors."
While Oxcart would continue in secrecy, the YF-12A test program would be done with a certain amount of media openness, which brought the benefit that if someone happen to spot an A-12, it could just be attributed to the YF-12A program. Also, at the time of Johnson's announcement, there actually were no YF-12As at Edwards, and the timing of the announcement actually caught the program folks a bit off guard. Two aircraft were then hastily flown to EDW, and according to local lore, the aircraft were shoved into the hangar so quickly after landing that the residual radiant heat set off the hangar's fire protection sprinklers.
Then five months later, on September 30, 1964, the media was invited out to Edwards to watch a YF-12A fly as well as to see one up close, and the four AP shots were taken on this visit. While the wirephoto of the low pass isn't clear enough to distinguish the tail number, the display aircraft was the last YF-12A built, 60-6936; this plane was lost on June 24, 1971 due to an inflight fire. Both crewmen ejected safely near Edwards.
If you want further information on the history of the Blackbird program, check out this amazingly detailed timeline PDF.