In the salmon example, I would consider it inappropriate to take as many pictures of salmon as possible and try to get them shown to as many Brits as possible. I wouldn't, however, ask a business selling fish in America to not use salmon in their advertisements. In other words, the negative utility of creating such images is non-negligible, but it is small enough that it can be outweighed by other factors. In the case of Mohammad, however, I have never in my entire life been in a situation where I had a particular need to depict Mohammad visually. Most depictions presently seem like deliberate attempts to antagonize Muslims, which I consider immoral. People do it, of course, because of in-group-outgroup behavior. If the alien arrived in England in 1812, Americans would be making as many photographs of salmon as they could.