Well for the thing about if you put your card in his cam,you could make a second folder on the card,so it would put all his in that one. Then before he takes any pics,change the record folder, its in the set up screen under the memory section, second one on the list under format the card. As for on the computer,just put them in different folders. I know it saves them in seperate folders each time you upload them,each is dated then numbered. That is unless you use some other program to get the pics off,than the one that came with the camera's. I usually keep them in one folder dated for the day they were shot on. Even when I take some with my mom's camera, and it has numbers of pics that match some of my older ones. By being in folders by dates they dont overlap. If it ever happens that the numbers are close,just make a subfolder for his.