When I started to learn Python, I worked on an image viewer application called HenWer. I found an open-source image viewer, ManWer, and I extended it with some extra functionalities. As a Python newbie back then, I enjoyed working on it very much.
Now, several years later, I wanted to use HenWer again. However, it was written in Python 2 with wxPython. I could make it run, but some features stopped working (e.g. zooming). It was also a bit complicated to install wxPython properly.
So, I decided to write a new image viewer (called JiVE) from scratch using modern technologies like Python 3 and PyQt5. HenWer had some cool features that I took over and I also added several new functionalities.
JiVE is designed to be cross-platform. It is tested under Linux and Windows. I couldn't try it on Mac, but it should work on that platform too.
A unique feature of JiVE is that it allows you to browse online images just as if they were local images. We can say that online images are first-class citizens. For instance, you can provide the name of a subreddit. JiVE extracts all the images from the subreddit and then you can browse among them with the arrow keys. Local and online images are handled the same way.