All WordPress pages + posts have an element in the editor called Featured Image. It’s located in the right sidebar, typically near the bottom. (Though this can change depending on what plugins you are using.)
Social media sharing
The biggest reason that I recommend site owners use this function is because it is what most social media platforms use when a link is shared on someone’s feed, even though the Featured Image is typically used as a hero image for pages + the thumbnail image for post excerpts/teasers in theme design.
Some bloggers add an image to the front of their blog content to mimic the look that a real Featured Image would have without realizing they could take advantage of this baked in function.
The problem with that technique is that other sites (like social media platforms) don’t realize the first image is the most important one. so they will either think there is no image to show at all, or scan the entire page for graphics, likely landing on the logo as the very first one + display that instead.
So when you see a blog post shared + a perfectly proportioned graphic displayed with it, that’s because the author uploaded + set a Featured Image to the post.
*This can be overwritten by some social media/SEO plugins.
Replacing images on Facebook
If you have a new Featured Image to use, but it’s not showing up on Facebook yet, all you need to do is tell them you’ve updated the page.
Head to their debugger URL + paste in the page or post you want to update, then click Debug.
Note: the page/post needs to be public for this to work.
The results will show the details of the page as it will be shown on Facebook, including the available image. If it’s an old image, click the Scrape Again button that’s a few lines below the URL that you pasted in.
Once the debugger tool runs again, you’ll see your new Featured Image in the preview graphic. And that’s your cue that anytime you or anyone else shares the link on social media, the right graphic will show.
*If you update numerous pages, you’ll need to do this step for each page individually. The Scrape Again button only triggers Facebook to scrape the specific page you linked to, not the entire site.