Abstract: Methods of embedding and detecting a watermark into-from a digital image are disclosed. A method of embedding a watermark in accordance with an embodiment of the present invention into a digital image, the method comprising: generating a difference from an original image; segmenting said difference image into sub-regions; and calculating a watermark block into each sub-region by adding said watermark block with pixel values of each sub-region.

Abstract: A device for measuring the visibility, or diffusion coefficient, of atmosre air, including a light source for directing light onto a volume of air and a receiver capable of measuring the flow of light diffused by the volume of air. The source is surrounded by ambient air and furnishes a beam diverging in essentially all directions except within at least one dark cone. A receiver opening is directed toward the source, but is located in the dark cone so as to receive only diffused light. The apparatus is for use in meteorological installations, notably in airports.