Magneto-optical methods allow us to observe the dynamics of domain wall motion, but this is intrinsically a very noisy process. We discuss a new method allowing us to reduce the measurement noise, taking advantage of the acquisition of a whole temporal sequence of images. The resulting avalanche distributions give interesting hints as to the magnetization dynamics, but are strongly dependent on the size of the observation windows chosen. We investigate the effects of window size by studying finite-size scaling, and use this to extract the fractal dimension critical exponent 1/σν. © 2009 IOP Publishing Ltd.