Hello @AFMarshall ,
If the image used in another email or campaign type isn't in your Library, it likely means it was added via URL. I'd recommend copying the original campaign so you can open up the editing page and figure out either what the exact name of the image file is, or what its URL is if it was inserted that way.
Otherwise, right-click the image and select the Open in New Tab option from that pop-up menu. Then Save As the image to your device, and re-upload to your Library for continued use.
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