What determines the presence / absence of images in preview of links when you paste it in Facebook?

When writing a post in Vkontakte, inserted link. Then there is its definition and the editor shows preview of the image taken from the page. After the post published, there is only one link, no picture.
Should be something like this:
8b8a5e9fce8a4685b0b1c19bb32b1366.jpg
And it turns out like this (a link without an image):
48dc079cfec74a919b0afa1053ce5274.jpg

Prescribing a particular image using link rel="image_src" in the head - the problem is not solved. The editor takes it, but then when sending does not display.
July 9th 19 at 11:10
1 answer
July 9th 19 at 11:12
Solution
Thank you for help. - Lucie_Howe commented on July 9th 19 at 11:15

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