1. A method to automatically screen for the presence of a polyp in a body lumen, said method comprising: capturing at least one image frame from within the body lumen using a swallowable autonomous imaging device; generating a gradient map of the at least one image frame; automatically identifying, using a processor and the generated gradient map, an elliptical form; comparing, using a processor, the color of the elliptical form to one or more predefined colors to differentiate between elliptical content and elliptical polyps; comparing, using a processor, the size of the elliptical form to a predetermined size parameter; and automatically classifying the elliptical form as content, polyp or neither in accordance with said color and size.