Your monitor may be 1600 x 1200 but if it is a modern digital camera it may be the photo is 3648 x 2056 or something like that, so more pixels than your desktop.
So if you select Tile or Centre it is only showing part of the photo as the photo is bigger than the monitor desktop.
When you select stretch then if it is a "square" photo (3x4 ratio) then it is trying to stretch a "square" photo into a widescreen shape so that is always going to happen.
You need to open the photo with some sort of photo editing software and change the pixel size so it fits better on your monitor (try playing around with different pixel sizes).
If you want to display a "square" picture on your widescreen monitor you need to use a photo editing program to "crop" the top and bottom off the photo so the photo becomes more like a widescreen "shape". Then it wont look so strange on your widescreen monitor.