As a step to a better understanding of my options for configuring ArcGIS Pro Pop-ups with an Image, I have gotten as far as right-clicking on a layer, choosing Configure Pop-ups to open the Configure Pop-ups pane, and clicking the Image button to see an Image element on that pane:
I then click the pencil button to edit the Image pop-up element where I want to attach the same image from a URL to every feature.
To do that I thought it might be as simple as finding an image at Wikimedia Commons like https://commons.wikimedia.org/wiki/Ship#/media/File:DANA_2004_ubt.jpeg and copy/pasting that URL in as the Source URL:
but when I did that, and back arrowed to test it, the pop-up that appeared was as below:
How can I get this pop-up to show me the image that I tried to link in using that URL?