Old magazines are an abundant source of copyright-free images and illustrations. Simple black-and-white line art was popular because it reproduced cleanly. Line art makes a fantastic starting point for pop art inspired illustrations and can be picked up for pennies in secondhand bookshops and car boot sales. I’ve supplied all the scans to complete this masterclass, but feel free to source your own material. Scanning at them as 1200dpi Bitmaps is usually sufficient.