A scrambling method for Motion JPEG videos enabling moving objects detection from scrambled videos

This paper proposes a scrambling method for motion JPEG (MJ) videos and moving objects (MOs) detection from scrambled videos. In the proposed method, both scrambling and MOs detection utilize the property of the positive and negative sign of discrete cosine transformed (DCT) coefficients. Since a DCT sign is encoded separately from its corresponding magnitude, the sign is processed without decoding a MJ video. This feature makes the proposed method fast. Since this method only inverts some of DCT sign bits to scramble videos, the codestream length never change by scrambling. By this scrambling manner, the scrambling strength is easily controlled by the bit inversion ratio. Moreover, this method holds the relation of DCT signs between two frames to be able to detect MOs from scrambled videos. The proposed method can further scramble the detected MOs. In addition, descrambling never require either the position or the shape of the objects to be descrambled.