Visual image segmentation is the process by which the visual system groups locations that are part of the same object. Can knowledge of objects influence image segmentation, or is the segmentation process isolated from object information? The use of object knowledge at this stage of vision might seem premature, as the goal of segmentation is to provide input to object recognition. However, purely bottom-up image segmentation has proven a computationally difficult task, suggesting that a "knowledge- based" approach might be required. W e addressed this issue using two segmentation tasks: Subjects either determined whether a small 'x' was located inside or outside the region subtended by a block shape, or they determined whether two small x's were on the same shape or different shapes. The familiarity of the shapes was manipulated, and subjects were fastest to segment the visually familiar shapes. These results suggest that image segmentation can be partly guided by information about familiar objects, consistent with knowledge-based image segmentation models.