Trying To Upload Photos

A rather late reply. I use the drag and drop method on my MacBook Pro. I drag a pic from my photo album to the bottom right hand corner of the screen. I then open the forum site. I can still see the pic at the bottom of the screen, which I drag into the reply box.
I'm sure there are easier ways if you're IT competent but I'm not and this works for me on several forums.

 

https://www.thetriumphforum.com/threads/newbie-advice-for-pictures-and-avatars.23720/