The growth of networked multimedia systems has made digital data acquisition

exchange and transmission a simple task

but the ease of copying and editing also facilitates unauthorized use

misappropriation and misrepresentation

which makes it necessary to authenticate the multimedia data. At present

it has been a hotspot to authenticate digital images by the use of watermarking. According to the objectives of authentication

an image authentication system can be classified into complete verification and content verification. Watermarking for complete verification (known as fragile watermarking) considers image data as untouchable messages such that the data for authentication have to be exactly the same as the original. Content verification is a characteristic of multimedia data authentication. Watermarking for content verification (known as semi fragile watermarking) considers "information preserving" image manipulations

such as compression and format conversion

as acceptable. This paper presents the general framework of digital watermarking for image authentication

discusses the fundamental demands and common attacks

introduces various existing algorithms and analyzes their advantages and disadvantages. The paper also introduces the current state of the techniques and proposes several research topics at next stage.