I don't assign pics to my contacts, but I find the default green robot to be annoying. Any suggestions on how to change that default pic for all calls?
I believe that .png is located within the contacts.apk or the framework-res.apk, I can tell you for sure when I get home....if your device is Rooted, this would be an easy fix
you could also log into your gmail and add a generic type pic to every contact that calls you or that you call. if thats a small list, that's not too bad of a workaround.
but to make it permanent and as the default for all contacts, you will need to root and swap the .png file in the contacts.apk file like tparker was saying.