Sync grabs images using an option for max length of 1500px, so the super long images are just a smattering of pixels that barely represent the original image.
I can’t find a way in the app to get a better quality version. I end up opening a web browser to view.
If you open the comments up, and then open the image, the full size image is fetched.
TIL.
This should be the way for opening the image from outside of comments too.