Update: I figured it out.
chose unsplash as image source, search query was just "portrait orientation" then chose "fit height and maintain aspect ratio" in the sizing option.

update two: If anyone is interested. I got a response from Owen via email support. have not tried but he says
"If you use the Wallpaper Fusion source, you can add the "Orientation > Portrait" tag to filter them."

Original question here
I have two portrait mode monitors 2160x3840 but don't see a way to use an image source online that provides portrait images. I've read through the forum but don't see the specific answer. Do I need to use a specific url to load portrait images from online source? If so, it's Just not clear how to do this. Thanks. Really loving DisplayFusion.