Are pictures of guns offensive outside of the US? I realize growing up in the US with a family of hunters has me desensitized, but I can't imagine being upset at someone whose hobby is going to the shooting range.
Yes. The sentiment of many people in Western Europe [1] is that weapon-carrying Americans are at the very least somewhat lunatic.
Big disclaimer: this is not a value judgement, this is not a discussion I want to immerse myself in now ;). Just an observation.
[1] I don't know about other parts of the world.