The invention relates to a device (22) for evaluating an image (20) produced on a carrier material (8) by spot welding of a weld spot (19) using an optical image-detecting unit (23), comprising a camera (24) which consists of at least one detection means (25) and one lens (26). In order to create an evaluation device (22), by means of which the optical quality testing of spot-weld joints can be improved, the image-detecting means (23) comprises an illumination device (27) with a diffusor (28) for diffusively and homogeneously illuminating an image (20) of the spot-welding on the carrier material (8). Furthermore, the invention relates to a welding tool (1) for a spot-welding plant, in particular a welding gun (2), having an evaluation device (22) for analyzing an image (20) of a spot weld (19) on a carrier material (8).