1. A method of identifying one or more candidate polyps in an in-vivo image frame, the method comprising: receiving an image frame of a body lumen captured in vivo; determining one or more center points of candidate imaged structures, each center point defining a respective circle; computing polyp edge scores for a plurality of points around each center point, each polyp edge score measuring the coincidence of a respective candidate imaged structure and its respective circle; for each center point: detecting a plurality of edge points of the respective candidate imaged structure based on the polyp edge score; identifying a candidate imaged structure based on the detected edge points, and for each candidate imaged structure, identifying a candidate polyp for which extrapolating the detected edge points forms an edge in a shape approximating an ellipse.