How to shift image for comparison

If you're asking what I think you're asking, the answer would be to click on #2 to select it in the Finder, hold down the command key and click #80 to select a second, non-contiguous item. Now hit space to bring up Quicklook and click the "Index Sheet" icon in Quicklook, which will display the two images side by side. You can do this with as many images as you want, so long as they're all in the same folder.

Alternately, if they're both open in separate windows in Preview (or any other image editing/viewing app), activate Expose for that window (F10 I think is the default), and you'll see the open windows tiled for easy comparison.