Do you want to keep them as external URLs that are viewable in your app, or do you want to import the images into Mendix storage?
Mendix storage:
In a microflow you can import an image from a URL using the CommunityCommons function StoreURLToFileDocument
Keep as URLs:
Store the urls as a string. Use this widget to display your images: https://appstore.home.mendix.com/link/app/65122/
Thanks! This is just what I needed.