Not the vets job....Take it to the pound....
Legally if you find an animal you are supposed to report it to the local animal shelter and have scanned for a chip and/or have it posted as found on the many lost & found sites existing, now.
If it has a chip, it is to be returned to its rightful owners.
Many animals have been found years and many miles away from where they were “lost” [likely stolen] and returned to their owners.
As animals are considered “property”, same as your car, what if you left the keys in your Maserati and somebody “found it” and decided to just keep it?
Same legal principle.
When you find an animal you should make every attempt to reunite said animal with their owner.
Every day my lost & found groups post pleas from owners looking for their beloved pets, begging for it to be returned.
Many of them are breeds “most likely to be stolen” and it breaks my heart because the dog has probably been moved across state lines and sold for drug money, never to be seen again, barring a microchip miracle.
Others may have been found by somebody who now thinks how lucky they were to find that “free dog” and never intends to try to find its people.
That is not something I could ever personally do.
The guilt would kill me.
It should be a simple choice.
Do the right thing.