In the recent years, many breakthroughs are made in the Image Processing Technology, particularly in areas like satellite imaging and biometrics. This paper presents an experimental approach of vision based surface roughness measuring system using speckle images produced by a line laser beam on milled surfaces. A CCD Camera, line laser source and white light were used for capture the images of milled surfaces. A signal vector was obtained from image pixel intensity and it was processed using MATLAB software. Mean and standard deviation are the two parameters used to characterise the image signal vector. The roughness of the specimens, particularly the Arithmetic mean slope (Rda) are computed using a stylus instrument. From the experiments, it is found that mean intensity of the signal vector of the speckle line images correlate well with Rda values of the surface roughness. Hence, the mean image intensity value of speckle line images has a strong potential for the online characterisation of surfaces. © Published under licence by IOP Publishing Ltd.