A way of measuring the geometrical characteristics of progressive steep water surface waves is to use a visualization technique connected with image analysis processing. In the laboratory, visualization of wave profiles can be realized with quite simple procedures: a previous paper (Bonmarin and Ramamonjiarisoa 1985) has described a technique allowing such a visualization in a large water tank 40 m long, 3.2 m wide and about 1 m deep. This paper reported also on a manual process for analysing the wave pictures obtained. In the present paper, we describe an automated image analysis method which is complementary to the manual process mentioned above. It uses a video technique and allows analysis of a large number of pictures leading to statistical measurements.