I reported a bug a while back about images scaling to full screen. It was marked as fixed - but I am still encountering this problem from time to time. I can't seem to discern a pattern as to when an image will scale and when it will display at actual size - but I'd say probably about 10% of the time I am getting a scaled image. Sometimes if I restart Flow it goes back to displaying images at actual size and sometimes it does not.
To give an example, I am currently looking at one task where I gave someone a note on a 320x50 jpg - which is displayed at exact size when I click on it. Then the designer updated that jpg and uploaded the revised jpg a couple minutes later and the updated one is scaling to full screen (which makes it hard to review since that is probably about 6x scale). I tried restarting Flow, which corrected a scaling issue I was having about 30 minutes ago, this time it did not fix it.
If you need system info, I am using the app, on a Mac running OS 10.14.6.