The device (1) comprises means (7) for assigning, for each pixel of a second image, a part of the three components (red, green, blue) defining the color constituting the pixel, to a component alpha containing an item of information relating to transparency and allowing management thereof, in such a way as to obtain a coded image, and means (2) comprising a digital electronic card (9) which is formed in such a way as to decode said coded image so as to extract the information relating to transparency, and to merge this image thus decoded with a first image, while taking account of said item of information relating to transparency, the image resulting from this merging being displayed by appropriate means (5).