How to correctly specify a picture for publication on VKontakte?

Question

In contact with

Hey!
On my site I made (yes, as many do) social network buttons, aka "Share".
I took a script from Yandex (although it doesn’t really matter - https://tech.yandex.ru/share/ )
I press the "share" button, a standard window opens to post on the wall, in a group or in a private message and below the post itself . when the "add image" checkbox is checked, you can select an image from the page.
That's actually the question: by what criteria does VKontakte determine which pictures can be selected? There are far from all the pictures from the page and often there are not those that I would like. Maybe there is some attribute so that the contact accurately takes a certain picture? I would write it in the picture. Who faced, can you explain?

Answer 1

https://vk.com/dev/share_details - documentation.
Extract from documentation:

2. Illustration. If there are tags on the published page, og:image, twitter:image, imagethen the address of the image for the illustration will be taken from the one specified first, otherwise the first 8 tags will be taken <img src="...">, and from them those pictures are offered as an illustration, the size of which exceeds 130 pixels in width and height. If the image is larger than 537 pixels wide, then the link on the site will be accompanied by an enlarged image.