I have often found that using pre-existing images on paper or book jackets for sketches and work provides a deeper layering of my ideas where the pre-existing image is obscured partially or wholly in the image but has become part of the process of producing that image. This has developed into using whole books as kind of sketchpads, for example below I have used an academic textbook on Zoology. The sketches and ideas have been worked through with the text or images in the original pages. I have found these sketches are not only useful reference points for my painting but they have also become works in their own right.