This invention relates to a method to select, in an input image, pixels that can be watermarked by replacing their colour by a metameric colour. It comprises the following steps: correct the input image by applying a predetermined gamma law, convert the input image into a ‘metameric’ image in which the colours of the input image pixels are replaced by metameric colours, simulate the capture of the input image and of the metameric image by a camcorder in order to generate respectively a captured input image and a captured metameric image, determine, in a colour space and for each pixel of the input image, the distance between the colour of said pixel in the captured input image and in the captured metameric image, and select the pixels of the input image for which the distance is greater than a threshold. The invention also concerns a watermarking method based on metamerism.