The vision system developed for monitoring FSW process consists of a digital camera connected to a computer as shown in Fig. 1(b). The camera was fixed on a stand and all the images were captured at identical setting without zoom. The images were captured at the frame rate of 24 frames per second for the duration of 2 s after completing weld. The captured images were process using MATLAB software to identify the surface defects. The details of image processing are explained in following section. The weld joints were subjected to tensile test in order to assess the strength. The tensile test specimen was cut perpendicular to weld joint according to dimension in ASTM E8 standard. The tensile strength of each weld joint is given in Table 3.