A method for detecting a capsule camera entering into or exiting the GI tract, includes (a) taking a first test image under the condition that an illumination system of the capsule camera is disabled; (b) taking a second test image under the same condition as the first test image; (c) comparing selected corresponding pixel values of the first test image and the second test image to determine if a significant change in pixel values has occurred; and (d) upon detecting the significant change in pixel values, determining if the capsule camera has entered or exited the GI tract, and performing operations appropriate to follow such determination.