It's a miracle! As with most things tech-related, the solution turned out to be simple: Converting the format to .jpeg was the key (thanks, Inked), and then I had to attach the picture as an attachment, as opposed to copying it and pasting it into the body of the message. I had tried different things Chat GPT was recommending, and since attaching the image as an attachment never worked, I gave up on that approach, and tried pasting it into the body instead, before trying attaching it as an attachment after doing the .jpeg conversion.
Now that I can attach images, I'm going to play around with the quality and sizing settings to optimize the look of the image, so bear with me as I try a few different variations. Thanks again to everyone for helping, particularly to Inked. See, you're not as much of a Luddite as you think B)
Test #1 (bumped up the quality to the max):