You may have noted that in describing the algorithms previously, I have neglected to mention the training procedures for how these models learn. This omission is rather deliberate. As we will not be training any models, how the Viola-Jones method and the PICO method are trained to produce models will be left as an exercise for the reader.

Instead, in this chapter we wish to use already created models. These models are commonly used in practice. We will then compare and contrast the methods to find out their pros and cons.