Method and apparatus for inserting additional data into video stream without degrading picture quality

A method of inserting additional data into a moving image stream, according to some embodiments of the present invention, includes receiving a first coded bitstream, electing a first picture PA into which additional data is to be inserted from the first coded bitstream, generating a first picture PA′ by inserting the additional data into the selected first picture PA, selecting a second picture PB directly referring to the first picture PA, generating a second picture PB′ by transforming and coding the selected second picture PB in a manner that decoding the second picture PB′ obtains the second picture PB with reference to the first picture PA′ and generating a data sequence based on the first picture PA′ and the second picture PB.