Art Kane, a freelance photographer working for Esquire magazine, took the picture around 10 a.m. on August 12 in the summer of 1958. The musicians had gathered at 17 East 126th Street, between Fifth and Madison Avenues in Harlem. Esquire published the photo in its January 1959 issue. Kane calls it “the greatest picture of that era of musicians ever taken.”
— from the Wikipedia entry
The best thing about living in LA in the 90s was being able to see so many jazz greats play on random nights in small clubs, since lots of musicians ended up living where the recording studios were.