A presentation application is provided that allows a user to extract a portion of the foreground or background from an image. The user can define a polygon outlining a portion of the image, and can adjust the shape and width of the polygon. The presentation application may use the user-defined polygon to identify a background region associated with pixels lying entirely outside the polygon, a foreground region associated with pixels enclosed by the polygon, and a set of pixels that are initially unknown within the width of the polygon. The presentation application then determines whether each unknown pixel is part of the background, foreground, or part of both. Based on the classification, the presentation application can extract the foreground of the image and mask the remaining portions of the image.