Theft has remained a consistent problem in the art world since the dawn of civilization and spans from museums to art galleries to private collections. With the art market's value continuing to grow, the incentives to steal and engage in "art laundering" are only becoming more enticing. Enhanced security systems and improved legal protocols must be implemented if we are ever to see any change.
Art theft is a major crime, but it's immensely hard to sell a stolen masterpiece after a heist. If art thieves realized how hard it was to sell what they had stolen there would be far fewer art thefts in the world. This genre of larceny is not a cost-effective activity for most criminals.