Given a pre-image, you could use any single reflection, rotation, or translation, or combination of these transformations to re-position the pre-image on top of the image to confirm congruence. You would be able to visually see corresponding side lengths and corresponding angles measures are the same.
Under a reflection, rotation, or translation, an image is congruent to its pre-image. If the image can be shown to be the result of one of these transformations, then the image is congruent to its pre-image. Because of the transitive property of congruence, the same will be true if the image is a result of a sequence of these transformations.
