is it safe to use the same wire guage of speaker wire to run 12Volts power for cameras?

Not a good idea. Speaker wire is not rated for that application. Use Class 2 rated power cable.

thank you sir

http://www.bluejeanscable.com/articles/inwallrating.htm

In-wall speaker wire should be just fine. We've run 16g wire (stamped rated for 300V) many times.

If you are talking about that transparent sheath stuff, then forget it. I don't even recommend that stuff as actual speaker wire.

ok. thanks for all the inputs. :D