Why is the preview image not displayed in social networks?

Question

Facebook

Hello. help me deal with open graph reposting on Facebook namely: when I insert a link from Facebook, pulling up the first picture of the post, it seems ok - and when I do publish - the picture disappears. what is the problem ?
Is it possible to set which image to display? (sometimes the first picture on the page does not reflect the essence of the post...
the site on wordpress

here is the post link

here is an example of how it looks when published:

Answer 1

<meta property="og:image" content="http://site.com/example.jpg" />

<meta property="og:image:secure_url" content="https://site.com/example.jpg" />

<meta property="og:image:type" content="image/jpeg" />

<meta property="og:image:width" content="500" />

<meta property="og:image:height" content="400" />