Here is the idea. First you choose a photo, from your PC or an URL.
And then the software would apply a mask on it, like an opaque sheet but with a round shape window in it to show a specific region of the pic …
Of course the window can be moved throughout the pic to explore every details, using the mouse. And ideally one should be able to control the window size, or to zoom in it e.g. by +/-
This is a technique that can be implemented with a simple sheet of paper and scissors for prints. But I’d like to have a software for doing it on my PC for digital files. If you know where I can find something like that please leave a comment. If you are a developer and are keen to spend few time on that that would be great.