WP TIP 1
If you use more than one image in your posts, then use WordPress Publicize to automatically upload your post to Twitter, Facebook, etc, or, manually upload them, the image last inserted into your post, is the one that will be displayed on your media.
To avoid the wrong image being displayed, either:
Insert it LAST
Select it as your ‘Featured Image’
Authors especially would probably prefer their Book Cover being displayed, rather than some other, random, image.
WP TIP 2
If you opt for using a Featured image, or, have the same image appear more than once in your post (as I’ve done on this post):
You DO NOT NEED to upload the same image for each separate appearance!
Select the same image to be inserted wherever you want it to be shown in the post.
This will save taking up unnecessary space in your media storage.
WP TIP 3
If you post the same image(s) on several different posts, search for it in your media storage (using it as an images archive), select it and add it.
You DO NOT NEED to upload the same image for each separate post!