Ringo Starr has called on Paul McCartney, Yoko Ono and Olivia Harrison to sift through their private photograph collections for a new Beatles project: “If they’re listening ... dig out the negatives,” he said.

Starr was speaking at the National Portrait Gallery (NPG) in London, where a new display of recently found photographs that he took and then forgot about was going on public display.

The book features unguarded shots of Paul McCartney and John Lennon. Photograph: Ringo Starr/National Portrait Gallery

They include images of his fellow Beatles larking around and relaxing, as well as photographs taken on the band’s first visit to the US in 1964.

The photographs are being published in a new book but Starr thinks there are many more fascinating pictures taken by his Beatles bandmates that could also be published.

“The other boys had cameras too, so the next plan is I want to get the rest of my pictures, Paul’s pictures, Yoko will have John’s pictures, Olivia George’s ... it would make a great book. I’ll be in a lot more photos.”

He added: “If I put it out there, they might respond.”

George Harrison. Photograph: Ringo Starr/National Portrait Gallery

Starr said he discovered thousands of old negatives in boxes he hadn’t looked in for nearly 30 years. “I had a lot of stuff in storage and we had to move everything and I started finding books of negatives, a lot of them I didn’t know I still had.”

He said he had always been a keen photographer but was a late starter. “Growing up, we didn’t have cameras. I’ve got like six or seven photos from being christened until I was 18. Then I got into the cameras and now there is a lot of photos.”

Starr managed to get pictures of his bandmates looking relaxed and unguarded. “These are shots that no one else could have taken.” he said. “Together, they chart the story of four lads from Liverpool trying to live normal lives amidst the frenzy that surrounded them.”

There are 20 portraits going up in the display in the NPG’s bookshop. Each can be bought for £1,900 as part of a limited edition. The book is published on 21 September but can be bought beforehand from the NPG.

On the cover is a photograph of a young silky-haired Starr with a cigarette and camera taken looking directly into a mirror. “I like to say it is the first selfie,” he said.