First-World Problems: Uploading Pix From Phone to Computer

[dewline]

I have been trying to upload this one image file from my phone to my iMac so I can add it to the list I'm trying to sell on Facebook. Haven't really read it in decades, it's a giant coffee-table book about the Vietnam War with lots of images and an "Order of Battle" appendix, and the imagery and troop assignment data were what I thought I wanted it for. I need to be rid of it now.

I don't know why I can't upload the photo file.