Faststone https://www.faststone.org/FSIVDownload.htm Source: https://answers.microsoft.com/en-us/windows/forum/all/how-do-i-open-two-pictures-side-by-side/94ea5844-7aae-4baa-a75a-52dd0dfad950 Just select 2 to 4 images and press P to open the compare screen.