I wouldn't conceptualize it that way. The image isn't posted twice, it just shows up for more total members based on the gallery viewing options they make.

Put another way, if you put "portrait" and "fantasy" in the title of an image and uploaded it, it will appear for people who do a search for either "portrait" or "fantasy", because the image title is appropiate to both searches. 

In terms of gallery upload options however as they stand now, assuming this hypothetical image is in fact a fantasy portrait, when you upload it you can put it either in the "fantasy" or "portrait" gallery. Putting it in one will mean it will not show up in the other, even though it's appropiate to both in terms of actual content. 

In short then, what i'm suggesting is the same level of functionality that exits in the search engine be applied to gallery settings. The underlying principle I espouse here is that Images that are appropiate to more than one gallery should be allowed to be seen in more than one gallery, that is in all galleries for which they would be appropiate 

As for fears of a multplicity of viewings for the same image, who looks in more than one gallery at the same time?

The strong do as they can while the weak do as they must.