Use Advanced Custom Fields images as thumbnails in lists!
The last version of “Ultimate Post List Pro” supports the popular plugin “Advanced Custom Fields” (in short: ACF, see ACF at wordpress.org in a new window).
After you have created an ACF image field on the ACF admin page you can set that field as the source of the thumbnail on the list edit page.
That gives you a great flexibility in selecting which image is displayed at each post item.
Now you can choose the thumbnail from either the featured image, the first post image, a default image, the author’s avatar or the Advanced Custom Fields (ACF) image.