The aim of our investigation was to explore a new method of analysing flow images, based on the Optical Flow Technique. Conventionally, this technique was developed for detecting motion of large objects in a real world scene. Applied to the flow images, it appears to be an interesting alternative offering high evaluation accuracy without most of the typical limitations characteristic of FFT based PIV. Besides evaluation of tracer images, the new method was also tested with smoke images obtained from experiments both in a fluidised bed and in a wind tunnel. It was also successfully tested on an image sequence of a vapor bubble growing on a thin heated wire. The accuracy of the velocity measurements using the new implementation was investigated using synthetic particle image sequences generated with the help of a 2D numerical simulation.