As of July 17 at 11:59pm PST, Facebook will deprecate the ability to customize link previews, in an effort to reduce misrepresentation of link content. The changes will apply in Facebook natively, as well as to Facebook’s API integration partners, including Hootsuite and Buffer.
It will no longer be possible to customize the image, title or description of a link preview in Facebook profile or group posts. Pages will not be affected by this change until a later date.
Facebook pulls link previews from website metadata. If you share a link to a website that is not your own, be aware that it may not have this metadata available. So a complete link preview with an image may not be generated in some cases.