tweaked picture generation script to not rebuild built thumbnails
tweaked picture generation script to not rebuild built thumbnails

chris-blay/guillemot-core,USU-Robosub/Gilligan,chris-blay/guillemot-core,USU-Robosub/Gilligan,USU-Robosub/Gilligan,USU-Robosub/Gilligan,chris-blay/guillemot-core,USU-Robosub/Gilligan,chris-blay/guillemot-core,chris-blay/guillemot-core