Sooner or later, when working with images, you will find yourself in need of altering images: be it applying artistic filters, extrapolating certain sections, cutting, pasting, or whatever else your mind can conjure. This chapter presents some techniques to alter images, and by the end of it, you should be able to perform tasks, such as detecting skin tone in an image, sharpening an image, mark contours of subjects, and detecting crosswalks using a line segment detector.