When social posts contain a link to a website, they often display a link preview. The preview displays a summary of the content found at the link destination – usually including a title, description, and image.
Link previews are automatically generated, but each social network pulls this information differently from the link's website. This means that the final preview for a given link may not be the same on each social network.
Tweets will only display link previews when the link's website has Twitter Cards enabled. To verify if the site you're linking to has a Twitter Card (and to see what it will look like) enter the link into the Twitter Card validator.
To confirm that your Tweet contains an image, you can either attach your own or select a suggested image that's populated by the Post Console. Please note that, attaching an image will override the preview if the link has a Twitter Card.
For more information on Twitter Cards and how to add them to your website, visit this page.
Google+ posts generate link previews based on the data that Google extracts from each website. Add Google's code to your website to control link preview content.
LinkedIn posts generate link previews based on the data that LinkedIn extracts from each website. Note that These previews can be customized when publishing from the Post Console.
Facebook posts generate link previews based on the open graph meta tags (e.g. og:image) that Facebook's link crawler pulls from each website. If tags are missing or incomplete, the link preview will be incomplete.
Anytime you publish posts that link to these sites, Facebook will attempt to fill in the blanks with any available data. As a result, link previews may differ between posts.
Start by entering a link into the Facebook Sharing Debugger to see how the preview appears when published to Facebook. In order to generate a complete link preview, the Facebook Debugger flags missing meta tags and anything else that needs to be fixed on your website.
To ensure that your website is set up for optimal generation of link previews, visit Facebook's documentation.
Customizing Link Previews on Facebook
Posting on a Facebook Page enables customization of link previews only when: