Welcome. My usual tricks to fix image links for people did not work. Google wanted me to log in so it may be that the permissions are wrong on your end. You get brownie points for trying, however.
You need the URL to the photo itself - it will usually end with .jpg - and that is what you paste between the Image tags. You can paste the same thing into the address bar of a new browser window or tab. If you don't see an image there then you won't see it on LTG. If you want you can use Go Advanced and then Preview to see your post before it is posted. If you don't see the image there then it won't appear on LTG.
For the record I gave up trying to embed links to Google Photos and copied images I wanted to share to a Wordpress site and shared from there.
As a new user you first five or so posts will be Moderated so don't be concerned when they don't show up immediately.