I'm needing some help here. I would like to use a photo my wife took on her iPhone 11 as my desktop background on my iMac. She has shared it with me over email and messages, but when I select it as background image, it applies alright, but with a pop-up that says "low res image, a higher res can be had with transfer to disk" or something along that line. And the image is truly low-res. How do I go about a disk transfer of the image? Any help would be appreciated, thanks.