In today’s world of social media, where everyone’s every little thing is on display, it is sometimes difficult to recall a time when exhibitionism wasn’t ubiquitous and was, in fact, not admired.

Such are the inevitable thoughts upon perusing Kitty Kelley’s lovely new book — yes, lovely — about John F. Kennedy as seen through the eyes, or more accurately, the lens of her friend, photojournalist Stanley Tretick.

Kelley, notorious for her unauthorized biographies of such luminaries as Jackie Kennedy Onassis, Frank Sinatra and more recently Oprah, narrates the book, Capturing Camelot, which is essentially a photo album filled with about 200 images, including many iconic shots (John-John under his father’s desk), as well as many never before seen. The narrative provides just enough fresh information to justify yet another book about JFK.

Kelley inherited the photos, as well as memos and keepsakes, that Tretick kept in a trunk and left to her upon his death in 1999. Tretick once told Kelley playfully that the trunk was filled with nude photos. Instead, she found a treasure trove.

Kelley’s book is thus a story with many layers: Her own friendship with Tretick; his with the Kennedys; the Kennedys among themselves. Tretick’s photographs and notes provide a wider angle through which to glimpse the president and first lady, about whom we already know so much.

Is there anything left to know about JFK?

A picture is worth a thousand words, we have heard a thousand times, but some tell more than others. And sometimes the picture not taken tells us even more. These would include photos Kennedy specifically asked Tretick not to shoot. Not that Tretick always acquiesced but the relationship between the president and the photographer seems to have been one of mutual respect.

A photographer is perfectly positioned to reveal truths beyond the camera. He is essentially an authorized peeping Tom. Unlike the paparazzi who steals intimacy with a telescopic lens, the authorized photographer is invited to a most-intimate gathering.

Part of what one discovers, or rediscovers, about Kennedy upon reading Tretick’s notes is that the man irrevocably associated with womanizing (thanks in part to Kelley’s own expose in Jackie Oh!), was in most other ways a class act — humble, authentic, dignified and uninterested in being an object of adulation.

How refreshing and, these days, how rare.

In one memo Kelley fished from the trunk, he described Kennedy as “extremely polite, great sense of humor, quick as a rapier on the uptake, hard to top, cannot stand posing for pictures, expresses displeasure if he knows you caught him off guard in a photo that might not be to his liking … absolutely rebels at any photo that shows him eating or drinking.”

Kennedy also hated being photographed in hats because he felt corny and silly. Among more-contemporary politicians, President Obama seems to have harnessed this lesson better than most. Memorable in the annals of unfortunate headwear was, of course, then-Gov. Michael Dukakis, whose fate as a presidential candidate in 1988 may have been sealed by a photo of him wearing a military helmet and taking a spin in a tank.

Kennedy also objected to public displays of affection, which was commonly understood to be, well, common. Only people bereft of education and what used to be known as manners displayed affection in public. Whose business are one’s emotions, anyway? Ah. But they’re everyone’s today. We can hardly get through an hour without expressing to online “friends,” otherwise known as virtual strangers, our every waking experience, from what food we’ve consumed to who we spotted across the restaurant.

No one understood the value of image better than Kennedy, who defeated Richard Nixon in 1960 by a mere 100,000 votes out of 68 million cast, in part because he was surpassingly telegenic compared to the sweat-soaked Nixon. Even so — and impressively in our age of photo-ops and endless spin — Kennedy wanted nothing captured on camera that wasn’t real. If it didn’t happen, he wouldn’t pose and pretend that it had.

Again, refreshing and rare.

There’s no telling how Kennedy would have navigated our 24/7 media world, in which everyone with a phone is a photographer, and respect for personal space is nonexistent. As we ponder these what-ifs, one is grateful that there was once a Camelot, if only in America’s idea of itself, so beautifully captured by a remarkable photographer and given permanence by Kelley, who has a sweet side after all.