You can do this by using Google's photo editor called Picasa. The software has the ability to make collages of pictures you select to display them in the background as Polaroid alike pictures.
Download the application and install it accordingly then let it scan for pictures on your computer and select all the pictures you want to click on Create Collage. In the window you can set the result as a background or you can save the file to a graphical format (JPG, PNG, GIF, etc.)
