Watermarking compressed video data by changing blocks' prediction mode

The invention relates to a method for insertion of data in a block of image data, called the current block, of a sequence of images. The current block is coded or intended to be coded in the form of temporally predicted image data from prediction image data defined according to a first prediction mode According to the invention, the insertion method comprises the modification, according to the data to be inserted, of the first prediction mode into a second prediction mode different from the first prediction mode with a view to coding of the current block according to the second prediction mode, the second prediction mode being defined so that the prediction image data obtained with the second prediction mode are identical to the prediction image data obtained with the first prediction mode.