An ingestible pill platform for colon imaging is provided, designed to recognize its entry to the colon and expand in the colon, for improved imaging of the colon walls. On approaching the external anal sphincter muscle, the ingestible pill may contract or deform, for elimination. Colon recognition may be based on a structural image, based on the differences in diameters between the small intestine and the colon, and particularly, based on the semilunar fold structure, which is unique to the colon. Additionally or alternatively, colon recognition may be based on a functional image, based on the generally inflammatory state of the vermiform appendix. Additionally or alternatively, pH, flora, enzymes and (or) chemical analyses may be used to recognize the colon. The imaging of the colon walls may be functional, by nuclear-radiation imaging of radionuclide-labeled antibodies, or by optical-fluorescence-spectroscopy imaging of fluorescence-labeled antibodies. Additionally or alternatively, it may be structural, for example, by visual, ultrasound or MRI means. Due to the proximity to the colon walls, the imaging in accordance with the present invention is advantageous to colonoscopy or virtual colonoscopy, as it is designed to distinguish malignant from benign tumors and detect tumors even at their incipient stage, and overcome blood-pool background radioactivity.