Hi!
Yeah, in macOS you’ll need to use the command open, if you just give it the name of the file nothing will happen, as you can see in the error message it saids command not found, so it thinks that image.jpg is a command and not a file.
So inside the subprocees call just add the command open befor the name of the file. You can test it directly in macOS terminal to check that it works.

Hope it helps!
Diego