The golden age of cinema, which began in the 1920s and lasted four decades, was also a golden age for photography, when studio photographers captured the glitz, glamour and lifestyles of stars like Rita Hayworth.

Each one of the thousands of publicity stills taken by the Hollywood film studios to promote their latest films was shot with immense care and precision. Even shots like this one of starlets Dorothy Sebastian and Joan Crawford larking about on Santa Monica Beach in 1928 by Don Gillum were staged with care.

Many of these pictures are now part of the John Kobal Foundation and a new exhibition and book, Hollywood Unseen, has drawn some of the hidden photographic gems from its archive. Artists like Jean Harlow would have been contractually bound to be pictured whenever the studio desired.

Some show the film stars between shoots - here Humphrey Bogart is pictured on the backlot at Warner Brothers in 1942.

Others are more elaborate, with meticulous planning and choreography, such as in this picture of Joan Crawford joining in the Fourth of July celebrations in 1927.

There are also those that include family members. Here silent movie star Buster Keaton poses with his sons, James and Robert.

Others focus on the glamour and idealised view of the stars. Bette Davis was one of those.

According to Robert Dance's essay in the book some artists, such as Marilyn Monroe, revelled in the opportunity to pose for photographs.

Today the pictures have a life of their own. A photograph of Lana Turner posing with fishing rod and a tiddler has become an artefact that is now parted from the film it was taken to promote.

Stan Laurel and Oliver Hardy signing autographs for young fans on the set of their second feature film, Pack Up Your Troubles in 1932.

Harold Lloyd looks on as Buster Crabbe gives his daughter, Gloria, a swimming lesson at his Beverly Hills estate. Buster won a gold medal for swimming at the 1932 Olympics before becoming a film star.

Harpo, Groucho and Chico Marx outside the gates of the Los Angeles Studios MGM, 1938.

Of course there were also photographs taken on set. Here Montgomery Clift and John Wayne are on the set of Red River in 1948.

The whole process of film-making was recorded in exquisite black and white. Make-up artist Jack P Pierce transforms Boris Karloff into the monster for Bride of Frankenstein.

Burt Lancaster learning his lines in 1948 is one shot that is the equivalent of today's behind the scenes shoots with celebrities.