Need to identify this photo of gay men kissing on stairs

It's a rather famous photo, I think, which I think was taken in some gay rights demonstration in the 60s or 70s. In it you have people sitting on chairs: on the left there are two middle-aged men, dressed rather formally and looking serious, and to the right of them there are two younger men, dressed in revealing clothes and kissing each other. I've seen the photo before, and I just saw it in the documentary "We Were Here" (about how the San Fransisco gay community faced AIDS in the 80s), but I can't remember when and where it was taken, and by who.

is it "men kissing on steps, castro street"

That's it, yeah. It was take by Crawford Barton, apparently. And I misremembered the people on the left, it's actually a middle-aged mand and a woman. Still can't find any info when it was taken and what was the context, though. I'm pretty sure I've read some book where the context was explained, but I can't remember it.

http://images.tribe.net/tribe/upload/photo/afc/9cb/afc9cbff-2cda-4ce0-bca9-765bef4dc530

it's a lovely photo.

is that Harvey Milk's shop on the left?

Steps later rainbowed and then redone to conform to ADA standards.