In order to improve the security of a steganography system

an adaptive steganographic algorithm for JPEG images based on the block standard deviation of the DCT(discrete cosine transform)coefficients is proposed. Block standard deviation of the DCT coefficients can reflect the complexity of image regions. Therefore

a distortion function is designed according to rounding distortion

quantization step

and standard deviation. Then

the STC(Syndrome-Trellis Code)is combined with the distortion function to propose the steganographic algorithm. Distortion function can be more rational when block standard deviation of DCT coefficients is used in design. In this way

the total distortion of the image is reduced after embedding and the security is improved. Experiments show that the proposed algorithm possesses a better undetectability. The security embedding rate can be about 0.35 when the quality factor is 75.