1. A method for detecting polyp candidates in tagged stool or non-tagged stool images without performing stool subtraction, comprising: applying a filter to locations in image data of a colon including tagged or non-tagged stool to generate a response image based on a gradient magnitude, angle, and radius in relation to another location in the image data for each of the locations, wherein the locations are indicated in the response image as tagged or non-tagged stool based on their density or brightness within the response image; and selecting locations in the response image above a threshold as polyp candidates.