Considering the security requirement in this new digital world, image hiding methods are highly desirable in many digital image transmissions. In most of these techniques, the hidden information being undetectable by a third party is very important. Some of them try to overcome this issue by using a key which transfers through a different secure channel. In addition, less distortion in cover image after image hiding which leads to a more safe communication is also highly desired. This paper presents a novel image hiding method based on Chinese Remainder Theorem (CRT). This method not only is secure from a third party attack by using an undetectable key, but also has the least distortion in cover image in comparison with some other related methods.