On engine I can't see anything, only a small accumulation of water, maybe water to drain or leak beside base pump water or block??
I put other picture.
When the mustang is cold and off, I put water in radiator and begin to drip...
Update...
When engine is off, I was filled radiator and water leak as show picture (a lot time), then, I turn on engine and after 10 minutes engine warm up normally, and leak was to disappear, WHY? , what hapeened?
Heat expansion, perhaps? I can see a gap between the pump and the timing cover where it's supposed to mate flush against it. Buy a pair of water pump mounting gaskets ($0.89 each, usually) and a tube of blue RTV silicone. Remove the pump, scrape off ALL of the old gasket/silicone material, and apply a thin layer of fresh silicone to both sides of the gaskets before bolting the pump back up. Allow the silicone to cure for a few hours before starting the motor up again.
Also, while you have the pump off, it would be a good time to replace that short L-shaped hose - usually about $8.