This post is really just an experiment. I am attempting to use the URL from the image in this post for my cover image URL. If you see the same image at the top of my blog then it works. In that case, I expect to be able to copy the URL from the code while I'm in edit mode. If that does not work then I will try right clicking the photo for the link after I have posted.
OK, it works. When you are in edit mode you can get the URL after you have added the photo to the post by dragging it or selecting it. You will then see the code that includes the URL or address for the file.
NOTE:
The ideal size of a cover photo is 1920 X 300. If you try to check the size of the image in the preview while in edit mode, it will show what the image has been resized to so it fits the post, so if you know your image size that you loaded and it does not match the preview size, don't worry. The image will be the size you loaded for your cover.
Hope this helps someone.
Peace,
rob