Virtual Portrait is a free application for Windows that you can use to display a framed photo as your desktop background, just like you would in the physical world.
This virtual frame is resizable, and can be moved around the screen. You can even configure it to remain on top, so that no window will cover it.
Or, turn it into a dynamic virtual frame, adding photos from a folder on your computer that will rotate every so often.
All of this makes Virtual Portrait a great application - what are you waiting for? Try it out.