Is dumpster diving legal in Newnan, Georgia?

No, it is not legal.

"Sec. 17-43. - Scavenging.

No person other than the owner thereof shall interfere with any trash or garbage receptacle, cart or dumpster placed for the purpose of storing solid waste, or remove or take any of the contents thereof, or remove any trash or garbage receptacle, cart or dumpster from the location where the trash or garbage receptacle, cart or dumpster has been placed by the owner thereof."