MADRID -- Spanish authorities have slapped an export ban on a painting a day before it was due to be auctioned with a starting price tag of 1,500 euros ($1,780), saying it could be a lost work by Italian Baroque master Michelangelo Merisi da Caravaggio.The oil-on-canvas work apparently depicts the Biblical passage of the Ecce Homo, in which Jesus Christ is presented to the crowds before being crucified.