iPhone icons in SSH invisible

so everyone knows when you go into a certain place in your root folder of ios device, you can find all the graphics your iphone/ipod touch uses in its apps. so i go to this place (its different for some people so i wont put the hierarchy here), and i find all the apps like MobileMail.app and others. i'm creating my own theme and i wanted the pin from the maps app. so i went into ssh and found Maps.app and i see all these blank pngs. one says SmallGreenPin.png, but when i open it in preview it is totally blank and it cant be renamed or resaved. any one know whats going on?