Experiments on the behaviour of bubbles in a two-dimensional gas fluidized bed have been recorded on video and analyzed using image analysis technique. It is shown that these techniques offer the possibility to quantify local hold-up and all kind of bubble properties, such as size, shape and velocity, as a function of the bubble height in the bed. The accuracy of the technique is good and the results are in agreement with those reported in the literature. Special attention is paid to determining technique is good and the results are in agreement with those reported in the literature. Special attention is paid to determining shape properties of spherical-cap bubbles. The contour of these bubbles is decomposed into two circles, so that determination of the wake angle and wake area is possible. Both parameters are investigated as function of the bubble height in the bed.