There will be some voltage drop over the cable at 100ft. Here is what you can do:
Install near the camera a USB hub powered externally from a battery (not from the buss). This way the hub will raise the signal voltage on his end and the computer on the other end, so there will be less voltage drop. On the other hand, the camera will get power from the hub's power supply, so there will be no power loss over the cable. To power the hub you need to have a (1 Amp) 5V voltage regulator. I recommend a Low Dropout regulator and a 6V or 7.2V battery pack.