There may be an easier way than how I do it though.
You must have the photo hosted somewhere. that will give you an http address for the picture.
[ img]photo address[/img ]
With NO open spaces.
so the picture I posted above would be:
[ img]https://tegutalk.com/attachments/20180223_123201-jpg.12575/[/img ]
Close up the two spaces I left open - after the first [ and before the last ] - for the example and you get -