The man was slapped with the €90.15 fine after looking at a painting which had been left next to a rubbish container in Barcelona in 2011, Spain's 20 minutos newspaper reported.
The city's town hall said the man had broken municipal by-laws by rummaging through rubbish on a public street.
But Barcelona's public defender Maria Assumpció Vilàs said police had made no effort whatsoever to find out what had really happened.
She said the man involved had simply been observing the abandoned picture.
According to the man's version of events, four policemen surrounded him while he was examining the picture, and then fined him.
Recently Spain's central government caused outrage with draft proposals for fines of up to €30,000 for insulting a policeman and up to €1,000 for playing football on the street.