I don't think that's true. Did you try googling that? It wouldn't have taken very long.

I can't find a satisfactory answer. Wikipedia doesn't say. [1] says it comes from the print industry, but I can't find any indication that that's true (all the search results seem to be related to online, "hero image print industry" doesn't turn up anything useful). "Hero image etymology" isn't helpful either.

[1] http://line25.com/articles/30-web-designs-that-fully-embrace...