Selecting 2 files, the screen is split in two and you see each image in one part of the screen. Clicking on one or the other would allow to move/zoom the view of each file; and then a function to 'sync views' would make a movement or zoom in one of the views to be replicated (and scaled accordingly if the zooms are different) in the other.
An extra would be overlaying both files, with the top one at 50% of transparency, and also a function to show only the differences. In the overlaying mode, I guess some keys should be needed to select which layer is going to be moved/zoomed.
Nonetheless, XnViewMP is already great.
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Moderators: XnTriq, helmut, xnview