I've noticed a lot of posts recently where people have a URL/Link but can't get the image to post. Don't worry, I'm here to help, they key is show in the image below:
When you click on the "Insert Image" button go to the second tab "From URL" and then Uncheck "Retrieve remote file and reference locally" it should post right up after this.
This is one of a couple of ways to post images.
Questions? Let me know.