It seems to me that good lighting and focus are more important than resolution. With a saw we can't approach the resolution of even low res photos - if the photo is recognizable to the eye, then I feel like the saw should be able to reproduce it. But blurry images make it hard to get to detail around the eyes (the most important part of a human/animal image), and poor light balance makes the Gimp/Inkscape process break down. Much higher res images are slower to process in Gimp and Inkscape.