The Raspberry Pi will show (on the HDMI output) a small rainbow square in the upper right corner, when an under voltage is detected (check Power FAQ).
The first revisions of the Raspberry Pi have polyfuses (F1+F2) on the USB-A ports which limit the current. In later revisions these fuses were replaced by 0 ohm jumpers. However there is still a polyfuse (F1) on the bottom side under the micro USB power port. When powering the board via this port and a high current is drawn then the voltage drop through the fuse can get to high and problems can occur. See also the Troubleshooting Guide.
The Raspberry Pi camera is available in two versions. As normal camera with infrared filter and as NoIR camera without infrared filter. This means that pictures you take by daylight will look decidedly curious on the NoIR camera, but it gives you the ability to see in the dark with infrared lighting. Furher infos here.
Depending on the system USB+LAN can be deactivated/activated with the following commands:
echo 0 > /sys/devices/platform/bcm2708_usb/buspower echo 1 > /sys/devices/platform/bcm2708_usb/buspower
echo 0 > /sys/devices/platform/soc/3f980000.usb/buspower echo 1 > /sys/devices/platform/soc/3f980000.usb/buspower
If you do not have the permission, then run it with sudo, e.g.
sudo bash -c 'echo 0 > /sys/devices/platform/bcm2708_usb/buspower'