Sets a common thumbnail for posts that do not have a thumbnail set.
Edge Detail Settings

Settings
Enable Alternate Thumbnails
Set a common thumbnail for posts that do not have a thumbnail set.
alternate_images
Select a thumbnail image.
CMS Support Site

Sets a common thumbnail for posts that do not have a thumbnail set.

Enable Alternate Thumbnails
Set a common thumbnail for posts that do not have a thumbnail set.
alternate_images
Select a thumbnail image.