When you put a link on your Facebook Profile and click post afterwards you will get a description from your site and a clickable link plus a image.
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The image may not be the one you want as far as relevant to the content that you are sharing on your blog. There is a way to change this image with a couple of available images on your post that is a option if you do this procedure.
When you market on social media there are certain algorithms that you must follow & some concepts & tips that are needful to know.