Information hiding techniques become essential in a number of application areas. Digital audio, video, and images are increasingly provided with distinguishing but imperceptible marks, which may contain a hidden copyright notice or serial number or even help to prevent unauthorized copying directly.
The need for technical solutions to problems of digital media copyright protection, authentication, fingerprinting or annotation of digital contents has been raised. Copyright marks do not always need to be hidden. As some systems use visible digital watermarks, most of the literature has focused on invisible (or transparent) digital watermarks which have wider applications.
Digital image can be modified during transmission and this modification may affect the robustness of watermark which was embedded within it. To study the robustness of the image watermark embedding algorithms, the watermark image is subjected to various image processing attacks such as JPEG compression, Gaussian noise, rotation, salt and pepper, and cropping.
To reduce errors caused by channel noise and host signal modification, it is useful to apply error-correction coding (ECC) to the embedded data. Error correcting code can be utilized to correct the distortion of transmitted information.
This work is concerned with studying linear modulation and look up table embedded watermark algorithms in digital image. Both algorithms embed the watermark within the transformed domains (using DCT). The contribution of this work is to improve robustness of the best algorithm against different attacks (such as JPEG compression, rotation, sharpening …etc). To do so, suitable error correction code LDPC (low density parity check) scheme is to be used. the experimental result shows that when LUT algorithm applied as a steganography algorithms it give a high robustness against different attack (such as JPEG compression, rotation, salt and pepper, Gaussian noise) than a linear modulation embedded algorithm, so an error correction code (low density parity check) scheme is to be used to improve a robustness of LUT algorithms, and when the LDPC scheme used with LUT algorithms, the LDPC code increase the robustness of LUT embedded algorithms.