Danny Nicoletta’s first day on the job as a counter clerk at Castro Camera happened also to be the day of the Castro Street Fair.

Shopkeeper Harvey Milk didn’t have time to train a 20-year-old at the cash register, so he gave him three rolls of film and sent him out to shoot the fair. It was beginner’s luck that Nicoletta came across a flamboyant couple, one in leopard skin and blowing hair and the other in a Moms Mabley hat and a provocative T-shirt message across his girth.

That image became a postcard selling 5,000 copies, and 42 years later it is on the cover of Nicoletta’s first book, “LGBT San Francisco: The Daniel Nicoletta Photographs,” to be released by Reel Art Press this summer.

Though Nicoletta did, in the end, master the duties of a 40-hour-a-week clerk at Castro Camera, his trajectory was out from behind the counter and into the streets with a Pentax. He followed Milk through his election as a San Francisco supervisor in 1977, through his murder in 1978, and every aspect of gay life to follow. The last picture in the book, taken in 2015, was shot four doors away from the first picture, taken in 1975.

“I had a strong calling to document the journey of the LGBT civil rights movement and had the good fortune to be able to stay on that beat for the entirety of my career,” says Nicoletta, now 62 and living in Grants Pass, Ore. But he still has a 415 phone number, and he will be back in the city for a slide show and a book signing in August.

The $60 coffee-table book runs 300 pages and weighs 5 pounds. Half of the images have never been published or exhibited. But filmmaker Gus Van Sant had been to Nicoletta’s Fell Street studio and had seen the pictures on the wall. When Van Sant started production of his biopic “Milk,” he hired Nicoletta as consultant and special photographer on the set.

“Danny’s photos are a treasured artistic record of the people who initiated a movement from within their own neighborhood,” Van Sant wrote in the foreword to the book. “They were examples of the real people and places and influenced our vision for the film in innumerable ways.”

Some scenes were precise re-creations of still images by Nicoletta. During filming he shot them again. In the book these appear side by side, nearly identical.

These include a picture of Milk dressed as a circus clown hanging off a cable car on May 21, 1978, and a picture of Sean Penn as Milk re-creating that scene on March 22, 2008.

That didn’t make it into the film, but the portrayal of Nicoletta by Disney star Lucas Grabeel did. The set of the front counter of Castro Camera was built based upon a color image Nicoletta took with his Pentax.

There is a spread of Grabeel sitting at the desk, authentic adding machine, Pentax and Converse high-tops up on the counter. You can be sure every detail in that image is accurate. Nicoletta loaned Grabeel his trademark handmade hippie vest, which he wore to work every day for years, for the film shoot.

In the ’80s and ’90s Nicoletta shot the AIDS Quilt, ACT-UP, the alternative theater scene, leather culture, the nightclub scene and Jerome Caja, who painted miniature portraits in nail polish.

This century, the story became the struggle for international LGBT rights and for marriage equality. The photographer became part of that story three years ago when Nicoletta married his longtime partner, Michael Pinatelli Jr., at City Hall. Their eight-syllable hyphenated last name may have set a record.

The Nicoletta-Pinatellis live a quiet, rural life an hour past the Oregon border. His next book project is already under way: studio portraits of all the key players in the LGBT struggle, shot over the span of 10 years. The only key player unable to sit for his portrait was Milk, though Nicoletta did shoot a still life of the bloodstained suit he was wearing when he was assassinated.

“The thing that I would like to pass down to the next generation is a sense of hope, just like Harvey did,” he says.