When a link is shared in Facebook, Facebook will choose an image to show in the post. Â However, the image FB chooses may not be the best one for the purpose.
The Facebook Sharing Debutter atÂ https://developers.facebook.com/tools/debug/ can help you troubleshoot this.
Adding a link <link rel=â€image_srcâ€ href=â€preview-image-here.jpgâ€ />Â to the page header will define the image you choose here.
Alternatively, there are plugins to handle this for you.
Here are some links to help manage this issue: