建立了以JPEG静态压缩图像为掩密载体的掩密模型,给出保证绝对安全的掩密条件,并计算没有主动攻击情况下的掩密容量。根据JPEG静态压缩原理,假设只将秘密信息嵌入量化系数的最低有效位。将掩密模型简化为二进制信道,并证明了该掩密模型不能简化为二进制对称信道模型的原因是不能保证安全性。 Established a privacy model with JPEG static compression image as a secret carrier, gave the absolute security of the privacy condition, and calculated the secret capacity without active attack. According to the JPEG static compression principle, it is assumed that only the secret information is embedded in the least significant bit of the quantized coefficients. The simplified model is simplified as a binary channel, and the reason why this model can not be simplified to binary symmetric channel model is proved that it can not guarantee the security.