In earlier days of the Web, someone appeared to have hotlinked a photo from a page of mine, as their avatar/signature in some Web forum for another country, and it was eating up way too much bandwidth for my little site.
I handled this in an annoyed and ill-informed way, but which I thought was good-natured, and years later realized it was potentially harmful. I'd changed the URL to serve a new version of the image, to which I'd overlaid text with progressive political slogans relevant to their country. (Thinking I was making a statement to the person about the political issues, and that it would be just a small joke for them, before they changed their avatar/signature to stop hotlinking my bandwidth.) Years later, once I had a bit more understanding of the world, I realized that was very ignorant and cavalier of me, and might've caused serious government or social trouble for the person.
Sensitized by my earlier mistake, I could imagine ways that a subtly NSFW image could cause problems, especially in the workplace, and in some other cultures/countries.