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Managing Open Graph tags
Open Graph tags are used by most social media platforms to determine which title, summary, and thumbnail image to use when sharing content.
In particular, LinkedIn uses them when you share content in your activity feed or when you insert a link in a message.
When creating a media, you can retrieve the your content's Open Graph tags to automatically fill in the Title, Summary, and Picture URL fields by clicking the 
button after entering the content's URL in the Original URL field.
To do this, the source code of the page you are referencing in the Original URL field must contain the tags below:
<meta property='og:title' content='Title of the article"/>
<meta property='og:image' content='//media.example.com/1234567.jpg"/>
<meta property='og:description' content='Description that will show in the preview"/>
When you share a media in your newsfeed or in a post, LinkedIn will automatically use the values you enter in the media's Title and Picture URL fields to construct the thumbnail to include in your share.
Images used for thumbnails are stored by LinkedIn in their own cache system.
If you change a media's thumbnail after sharing or posting it, LinkedIn will use the cached version and the update won't be visible.
In this case, you should have LinkedIn clear its cache by going to the following page and inspecting the media's URL link:
Last modified 3yr ago