Image processing techniques have been used extensively in many different applications today. In particular, in fluid mechanics, image processing has become a powerful technique to study the flow phenomena, the flow pattern and the flow characteristics of two-phase flow. This paper presents a new application of image processing techniques to two-phase bubble/slug flow in a vertical pipe. Based on image processing techniques (image filtering for noise reduction, edge detection and thresholding for image enhancement, etc.), the results obtained are showed that this technique has many advantages. It is able to study together, in very short time, one image contains a large number of bubbles and the large amount of images, while the other methods such as point by point measurements technique or by using a digitizing table for digitization cannot be applicable. Moreover this technique also enable to identify automatically, to measure fast and relatively accurate the parameters such as size, shape of the bubble. These studies promise a great progress for an application of image processing techniques to study the complicated flow phenomena, the flow pattern and the flow characteristics of multiphase flow.