By Darren Waters
BBC News entertainment staff
The Federal Bureau of Investigation describes art theft as a "small but ugly criminal speciality" and estimates that artworks worth around $8bn (£4.5bn) a year are stolen around the world. As an exhibition of Edvard Munch paintings opens in London, can art ever be safe from thieves?
One of the most recent, and certainly the most high-profile, art thefts took place at the Munch Museum in Oslo last year.
Two paintings, one of them the iconic Munch work The Scream, were stolen by two armed men in August. They walked into the museum and simply tore the paintings from the walls before running to a getaway car.
The museum - which has more than 1,000 Munch paintings - has loaned a large number of works to the Royal Academy for an exhibition of the artist's self-portraits, which opens on Saturday.
Ton Cremers, founder of the Museum Security Network, says art theft remains a major threat around the world.
"According to Interpol and the FBI and Interpol it is the third largest illegal trade after drugs and weapons," says Mr Cremers, who offers a consultancy to individuals and institutions on issues of theft and forgery.
He says museums are the victims of theft in 15% of all art robberies.
"They are the ones in the headlines, private collectors are not."
He adds: "The awareness of theft and security has increased in the last 20 years. But too many museums rely only on electronic equipment, not realising that you also need a good security organisation as well."
British museums have a 'good level of security'
However, he says that British museums generally have better security than museums on continental Europe.
Since the 2004 theft in Oslo, the Munch museum has spent almost £3.5m on improving its security.
"The Munch Museum have gone very far with their security but it is still a good visitor experience," says Mr Cremers. "They have shown plenty of courage in taking this step."
Electronic ticketing, a security entrance similar to airport passport control, bullet-proof glass for the most prized works and a long hall which can be closed at both ends to trap thieves are among the measures installed.
"Everyone has to go through a metal detector and every bag has to go on a conveyor belt and is scanned," says Jorunn Christoffersen, head of information at the museum.
"Our main problem was the distance between the entrance and the halls, where very valuable paintings were shown, was too short. That is why we have made the entrance longer."
She adds: "Very few museums have sufficient protection if armed robbers enter.
Robbers in Oslo were seen carrying the pictures to a getaway car
"It is much more difficult in buildings like Tate Modern which are so big. You have to walk and walk and walk even before you see a painting."
Ms Christoffersen says the museum still has some concerns, including fears of a potential hostage situation if a robbery was attempted in the future.
"There is the danger of a hostage situation with so many obstacles now in the museum. Even if we have done everything to prevent this from happening."
With so many of its paintings on loan in London the museum has taken every step to ensure they are safe.
Should this familiar airport scene be repeated in all museums?
"Our head of security has been in close contact with the Royal Academy and is in London now. He is also meeting with security heads at other museums, including Tate Modern and Tate Britain.
"He has made sure the paintings are safe at the Royal Academy."
Mr Cremers says: "If you were a private collector I would say - don't tell people about your artwork, don't show them and keep it in the heart of the house.
"Museums have to do the exact opposite."
Tore Hoifodt, head of communications at DNV, the firm which carried out the security assessment at the Munch Museum after the theft, says no museum would ever be robbery proof.
"If you turned a museum into a fortress, perhaps it would be, but you want as many visitors in there as possible."
He says changes to the entrance at the museum, making it less open and less accessible, are measures which could be applied to all museums and galleries.
"Some people feel the museum is less accessible, but it is a difficult balance."
Mr Cremers says improvements in security techniques would further protect art.
"Access control will change. There have been a lot of improvements to showcases and new techniques in tracking the movement of objects around museums."