Not unique since its polo’s address and you have no way to make a unique signature with their address. You have no control over it, any more than the 1000’s of others whose withdrawals go through the 2 addresses.
Remember the BTC showing in your Polo account is simply from their database records and not some BTC address. Polo pools the Bitcoin from everyone’s account, and uses a system to do withdrawals through a number of addresses of the real BTC
No you do not. You have at best a screen shot of Polo’s withdrawal page.
BUT I can create the same image with all the correct info since the info is on the blockchain.
This is the problem. All the info that can be used to check your claim is on the blockchain available to everyone in the world. And can be used to create exactly the same images you can.
EDIT: If the address the BTC came from was your personal address then your arguments would be correct in the most part and you could prove things. The problem is its a shared address which you have NO access to and no control over if Polo would even use either address again to process a future withdrawal request