Is there a way to let one image be in two albums at once?
Moderators, be gentle. I have searched.
Yes, just tag the image with a keyword (or keywords) you wish to associate with a 2nd (or 3rd or 4th, etc.) album.
Then in the 2nd album properties use the exact string you used for the keyword to make the image with that keyword display.
Note, however, it will not be available as the thumbnail for the 2nd album, but it will display when the album is viewed.
See: http://coppermine-gallery.net/demo/cpg14x/docs/index.htm#album_prop for the album properties.
See: http://coppermine-gallery.net/demo/cpg14x/docs/index.htm#edit_pics for where/how to place the image keyword.
HTH