If a webcam must be used, get one with a physical on/off
switch and has "on/off" LED indicator. Another alternative
is to get a frame grabber card and buy cameras that can
be physically turned on/off w/LED and/or its power can be
turned on/off.
Also, be wary of any camera/microphone that is wireless based
w/o encryption or emits RF (analog) signals as these acts like
broadcast stations that can be directly "snooped". It is perhaps
it is more preferable to get LAN on/off w/LED cameras that encrypts
data over physical LAN CAT cables, and perhaps with PoE (Power
over Ethernet) technology.
Lastly, if you have no real-value needs (security/surveillance), then
don't bother getting cameras! Duh! ;)