I wouldn't mind testing Image Eye, but I usually like to test some programs as portable first.
The website says to install it first and then grab the executable if you want to run it in portable mode.
Edit: I tested it. It works a bit different to other image viewers. You have to open an image to access the main program and settings (Options). But it seems to work well. The default keyboard settings are slightly different to what I'm used to. For example, left and right arrow keys rotate the image instead of displaying previous and next images, but it can be changed in the options.
