You can copy and paste the URL of the blog page as your post. Facebook will create a summary lead-in text block and if an image is associated with the text will include the image. Sometimes the image is not correct or just not the one you really want to have associated with your article.
In the lower left corner you will see the images Facebook has decided to associate with your blog page. You can click on the + sign and add more images/photos, or click on Hide to remove images/photos.