A group of Italian Muslims had appealed unsuccessfully to the Vatican ( news - web sites) last year to have the fresco, by Giovanni da Modena, removed or to have parts of it covered, arguing that it offended Islam.
What are Muslims doing in a cathedral (belonging to an unfaithful religion, as they see it), anyway? See, if they had stayed away, they would never have known about it and wouldn't be "offended." Are they willing to take suggestions from non-Muslims about the decor of their mosques?