This paper proposes a possibility that add watermark after encrypt image, basically, interference of transmission may include: transmission signal error, voltage instability, hacker attack … etc, and these factor can cause distortion.
This paper studies the relationship between the original image and the decoding image that after processed similar DES encryption and add salt and pepper noise. This paper also compares the distortion phenomenon of original image and encrypted image, and derives the concept about quality control of images after encoding. Some experiments and results are discussed in this research.