The snapshot API takes an existing Image, which if non-null, should be updated with the result of the snapshot. This is not functional in the existing version since the implementation relies upon Image Ops (RT-17409). Once that feature is in, we will need to use it to properly update the image (currently a new Image is returned with the correct data, but the existing image is unmodified).

Based on the current proposal for Image Ops, the snapshot API will need to be slightly modified as well. The parameter and return value of the 4 snapshot methods will change to taking a WritableImage subclass of Image (for type safety).