Choosing image when I share article with Facebook

Please note that Facebook’s behavior is a bit different. It crawls the page to grab the data to be shared. We just pass the URL and then Facebook crawls the page and on that we don’t have any control.
You can specify the Title, image, URL or description to be shared using Meta tags only.
Know more about Meta tags –
https://support.sharethis.com/customer/portal/articles/475079-share-properties-and-sharing-custom-information#Open_Graph_Tags

Please let us know your site details so that we can take a look.

I resolved the problem
inserting pictures in a larger format on the article (at least 200px)
Thanks