  In this paper we introduce experimentally the phenomenon of speckle and its
interferometric applications. With the popularization of CCD sensors and
webcams, it is now easy to acquire speckles patterns, to reduce them and
exploit them. The material used here is what we could find easily in high
schools. All Image processing mentioned in this article could be done using the
free software called IRIS. Keywords are essentially diffraction, interference
phenomena and Fourier optics. After presenting the characteristics of speckles
we discuss the phenomenon of speckles interferences by analogy with the
conventional 2 and N waves interferences. Finally, we apply interferometry to
measure the angular separation between the components of a double star in
drawing heavily on the historical experience of Antoine Labeyrie.
