after opening and viewing a post, the Android "back" button returns you to the feed. However, the same behavior didn't work for opened images. Frustrating.

Yep, you can swipe up on the image to close it. Not the most intuitive at first but

I was going to ask about this too. It seems my mind is trained to just hit the back button after viewing an image to go back to the feed. This is a great app, please add ability to back button out of images.