How does wechat choose the link's thumbnail?

I have an issue very similar to this issue, and the accepted answer is outdated.

Currently, when users share a link to my website, 3 cases happen:

there is no image (default grey icon)
there is an image that is not the intended one
there is the intended image (the main article image, also referred in the meta using open graph)

What's more, different users, on the same network, sharing the same article, experience different results.

How does wechat identify which image to use as a thumbnail when sharing a link? How can one achieve a consistent behavior?

Solution

You have to have a Wechat platform account and use the jssdk provided.