How to Set Up a Backup Default Image Thumbnail
If you’ve got the Excerpts & Thumbnails add-on activated, you can set a default thumbnail for your feed source. This default thumbnail will be used whenever an imported feed item from this source will not have an image associated with it. The plugin uses the same default image from your Media Library for each feed item, it does not create a duplicate for each one.
To implement this functionality, we use the inbuilt featured image selector from WordPress. Again, it’s just like adding a featured image to a post, only this time that image will be used in generated imported feed items’ thumbnails.
Default thumbnail image
From here you can choose the image you’d like to use as the Default thumbnail image. You can choose one from your Media Library or upload any other image.
Default thumbnail image preview
Here you’ll be able to view a preview of the Default thumbnail image you selected further up on this page.