Photo Gadget Viewer is a free to use program for Windows made for browsing through digital photos. It is fast in opening a photo file and offers standard keyboard shortcuts to look at other photos available in the same folder. Mouse wheel works for navigation, too.
Thumbnails view shows all photos in the current folder and to get to a single-photo full screen view simply double click on it. Auto-rotate option based on EXIF is enabled by default. If you open a selection of several photos the program will browse only through that selection. Photo Gadget Viewer can sort photo files by name, date or size and includes an option to open a photo with an external program.
You can use Save As option to make a copy of a photo or convert it to a different file format. In the settings dialog you can select photo file extensions that you want to be associated with the program so that it opens those files directly on double click. Supported formats include JPG, BMP, TIFF, PNG, PCX, and TGA.