Hundreds of authentic ancient Greek shield patterns, organized by time period, mostly for Hoplons but some for peltes as well. (My knowledge of Greek plurals is abysmal. Please pardon the obvious errors.)
My first attempt was to reproduce them by hand with a small brush. That took an excessive amount of time for mixed results so for the next batch of hoplites I downloaded the images, scaled them down 80%, printed them on a colour laser printer (a big "thank you" to my employer of the day) and cut them out. Because the images are flat and model hoplons are convex I cut a slit, usually at about the 5-o'clock position, soaked the back in PVA glue and applied them on the shields. The slit allowed the paper to conform to the shield, overlapping perhaps 1mm at the rim. The distortion is unnoticeable at arms length.