Stardust Image Viewer 2003 lets you easily step through images in a directory.
16 image types including JPEG-2000 are supported, and you can set all images to the same zoom level, or all images to fit the window.
Won't interfere with other image viewing software; easy install/ uninstall.
To get started with Image Viewer, click the toolbar Open button, or select Open from the file menu. Then, navigate to a folder that contains images you would like to view. Select any image in the folder, and open it. Image Viewer will immediately display that image, and you can use the Previous and Next buttons to move through the other images in the folder.
Since your images may be of different sizes, once you've opened your first image, you may want to set Image Viewer to fit all images to the window size. Just select Fit to Window from the Zoom menu - the current image will immediately resize to fit the window, and all other images will resize to the window as you step through using Previous and Next. You can even change the window size, and images will still fit it perfectly.