Digital images and videos are so ubiquitous nowadays that it would be difficult to live without them in the heavily digitized and networked world. Various digital devices, such as digital cameras, camcorders, scanners, digital televisions, personal computers, mobile phones, and printers, rely on digital image and video processing and coding technologies. Despite the extreme usefulness of digital images and videos, there are more and more concerns about security and privacy rising from a heavy dependence on digital images and videos: how to protect sensitive information recorded as digital images and videos from unauthorized access and misuse? Different people may have completely different reasons for having such a security concern. For instance, digital content providers are worrying about pirate copies of their products, end users want to keep their private images and videos in their mobile phones and their online web spaces safe from unwanted hands, and governmental/military/diplomatic bodies need to carefully protect classified documents (many of which are recorded in the form of digital image and video). All of these demands require content protection and access control, which can be fulfilled by applying cryptography to multimedia data, that is, by encrypting digital images and videos and by defining who can access the encrypted contents.