The problem is you posted a link on Facebook, but Facebook is not displaying an image for that link.
This problem can be caused if Facebook was unable to scrape the page for the link.
You can see how Facebook scrapes the page by using the link debugging tool.
If Facebook was unable to retrieve the page the first time, no image will be displayed with your link.
You can have Facebook retrieve the page again. If Facebook is successful, you will see some images. Give Facebook some time to update, and then the image should show under your link.