I find FastStone Image Viewer a useful freeware to compare 2 images side by side, by selecting the images (by holding down Ctrl and clicking) in its Browser view, then pressing P.
Is there a command-line option to directly compare images as above? e.g. something like
"C:\Program Files\FastStone Image Viewer\FSViewer.exe" "D:\image1.jpg" "D:\image2.jpg"