Welcome back @hoglahoo! You skipped the entire year of 2016? That must have been one furry face mitten!
How do you upload a picture file in a private message? Not using the URL-to-a-picture option but actual upload a file. Like in this box I'm typing in right now it has a upload a file button but in a private message I don't see that button anywhere. I've been gone from here for a long time but I distinctly remember it being an option previously.
Iirc you cannot attach pictures to private messages. You would have to stick a link to an outside site.