Webshots fits each image to fit your screen. However, if your monitor is not 16:9 you will get some edges of the image cropped off.
To access the settings menu open the Webshots application and click on settings tab at the top right of the page.
From there you will see an option to "Scale Webshots Photos to fit Desktop" and "Scale personal Photos to fit Desktop / Wallpaper". Depending on which type of image you wish to effect, change that setting to "No". Then, go to the Desktop Background settings in your computer's personalization menu and select "fit" for "picture position". If you are not sure how to find those settings type "desktop background" into the Windows start menu and press enter.