We can of course use the following to set the default share image:
<meta property="og:image" content="http://website.com/images/icon.png" /> However, is there a way to set it as a fallback only, instead of a default? Meaning, only to be used IF Facebook can't find a larger, more appropriate image to use from the blog post.
Note - Facebook already scrapes on its own automatically without any help from the website owner to try and find the most appropriate image. Only, if there's not an image used or too small of one it would be nice if it used a user-defined fallback instead of some other non-related arbitrary image found on the page.
A better understanding of what criteria is set for the Facebook share scraping bot would help a lot. Or if it were possible to simply specify to only collect an image from a specific div ID or class and that if none is found to use the fallback.