Windows 7 features an ability to rotate wallpaper after specified duration. Now, ZapDEV (translated page) is a freeware tool to manage your wallpapers on Windows which has pretty good features to have a custom wallpaper out of your photo collection. This tool allows you to easily rotate wallpapers after a specified time and on top of this, it allows you to give effects to your wallpapers like Polaroid, center, optimize etc.
There are two tabs for the application, one is the photos tab where you can provide the folder of photos which you want to show as effects on the main wallpaper and in the second tab you can select the folder where your wallpapers are stored. You can also opt for a black background.
You can set the borders and also the size of the photos on top of the wallpaper. You need to specify the time in seconds after which the wallpaper is changed. A simple and useful tool to create wallpaper mashup for your desktop.