GreenScreen : A visual effects technique for compositing (layering) two images.
The technique has been used in many fields to remove a background from the subject of a photo .
Steganography : It is a tool to conceal image within another image.
* [ For both above tools the images must be of same size so that no cropping is required ]
Reverse Steganography : It is a tool to extract image hidden within another image.
Filters : Image filters - Grayscale and Red Shading