To create this Masked Liquib scene a photo of trout in an aquarium was first loaded.  Then the Set Mask Stencil/Background option was used to automatically create a Stencil based on that image, and also set the picture as the Mask Background.  Another much more colorful image was then loaded and manipulated with various Tools and Effects.  The result is that only the dark areas of the aquarium photo remain unchanged, while the bright colors show through the lighter portions.