The work by Bruce Bairnsfather, the creator of the cartoon character Old Bill, was found by a curator in an old box at Dunfermline Museum.

The picture depicts a soldier in an embrace with a girl. Both of them are wearing anti-gas goggles. The caption says: Of course no doubt the war will affect romantic fiction.

It was published in London in Bystander magazine on December 4, 1918, and later in a book called Fragments from France.

The picture, a monochrome watercolour, went missing after it was sold at an exhibition of the cartoonist's work in 1919. It is not known how it ended up in Dunfermline.

Lesley Botten, the museum's acting collections co-ordinator, said: "When I first realised what it was I was astonished. I was looking for something else and recognised the picture but I did not think it was an original. It had been taken out its frame but was signed in pencil. It was signed and dated by Bairnsfather."

The find has excited art experts even though the picture does not feature Bairnsfather's most famous creation, Old Bill.

Mark Warby, an authority on Bairnsfather, said: "It would be great to know how the museum came to have the picture. They come up now and then in auction. He was the greatest cartoonist of his time. His success was phenomenal."

With his walrus moustache and blob nose, Old Bill epitomised the British soldier. Bairnsfather, a captain in the Royal Warwickshire Regiment, originally drew the character when serving on the Western Front.

He continued producing cartoons, which were published in magazines, books and tobacco advertisements, after he was invalided out of the Army.

One First World War general described the artist as the man who kept the Empire laughing in its darkest hour.

Old Bill, the Tommy who could "size up officers better than any Sherlock Holmes" became a cult figure. Bairnsfather's 1915 picture of two unhappy soldiers in a shell hole with the remark "Well if you knows of a better 'ole, go to it" was his most famous work.