I have a blog on Wordpress.com. I would like to have it set up in such a way that when I make a post on the blog, I can select an image that I want associated with that post so that every time someone references that post on Facebook or a similar site, that individual post's selected image will appear as the thumbnail.
I tried to research myself what needs to be done - but I found the results of the web-search to be profoundly confusing. I have no idea which premium features I need to purchase (and due to budget limits I don't want to purchase more than necessary) I have no idea which theme or themes support this feature - nor do I have the faintest clue how, when authoring the post, to specify the image.
Can anyone make this information clear?