Note: Facebook determines the preview images of link posts that are links of Facebook pages, groups, albums, events and posts.
There are many different reasons why you may need to use a custom image when creating your link posts. In order to create your link post with a custom image you’ll first want to locate both the link that you want to share as well as the image you are wanting to have shown when the link is posted. Once you have those two things go to the Schedule a Post page and paste your link into the link box and then click the link button:
Once you click the link button you’ll see a message that indicates CinchShare is loading the graphics from the link you pasted. You’ll be able to select one of those images located on that page or you can choose to provide a custom image instead. Simply click the “Choose File” or “Browse” button under the Upload Photo label to select your custom photo from your device.
Now you can see that my link is still loaded in the link box and now my custom image is selected as the custom photo that will be delivered with my link post.
Then when the post is delivered the custom image is displayed as the preview image to the external link.