Thanks so much. This almost works perfectly. The border is around just the image, which is what I wanted, so check there. I don't want a rounded border so I set the border-radius to 0. Check there. The last small detail is that the border only appears on the left and right side of the image, not the top and bottom. If I adjust the second translate property to -49% I can get the border on the left, right and top, but not the bottom. Similarly, if I set the second property to -51%, I get a left, right and bottom border, but no top.
Ideally I'm looking to get a border on all sides of the image with a border radius of 0.
Thanks for all your help with this. It's already a big improvement and I am very grateful for your solutions.