To overlay multiple pictures, you can use the HDR option. This option can be found on the main screen on the application between Stick option and Open Browser. When you click the HDR button, a new windows will be opened. In order to overlay several images, they all have to be the same dimension (like 800 x 640). After you added the pictures, you can set the Brightness, Saturation, Smoothness, Contrast and Detail. To finish, click Done.