I have a MacBook Air. When I want to post/upload pics anywhere, I open photos, then I choose which one I want to send/post, then when I have the cursor on the chosen small photo icon I press on the track pad with one finger and 'drag' the photo to an area on the desktop with another finger! Sorry, it sounds odd, but it works. When I want to post/upload a photo, from the options -computer, file or desktop- I choose desktop. It works for me on my Mac.