>publicly funded entities should not give benefit and preferential treatment to private and proprietary enterprises and systems.
It wouldn't be a "gift" from the USPS. It would be a mutually beneficial financial contract. (E.g. 5 year multi-million dollar contract to mount Google cameras.)
Similar to how private events pay the government for extra police officers to direct traffic or supplement security. Or how the Pentagon charged the Top Gun film production $25,000 to turn an aircraft carrier around.[1] Government entities have set the precedent that they will sell services to private companies.
The citizens' access to the USPS photos would a given and be part of the contract.
[1] https://www.quora.com/Why-did-it-cost-25-000-to-turn-the-shi...