At whatever place you are looking for in adding the image to a person, you can:
1 - Add New Media - (add any media your computer can access on your compouter via Windows Explorer)
2) - Link Media - whereby you are presented with a list of media already in FTM and you can add a link to that photo to your person. This will not create a second copy of the media.
The above can be done at:
People > Family > Media button in right pane.l
People > Person > Media button in button row below where facts are listed and above where notes begin.
(You can also add media to a source or a fact, but that is not often done).
Perhaps the quickest way to add the photo is to add via attaching it to a Citation of a Source. Then, copy the link to the citation to the same fact for the 14 people (like to the marriage fact if the picture was taken at a wedding, or you could even setup a Custom Fact for "photo" and attach the source citation to it. Only one pic will be added to the FTM file.