Welcome to CT! That is what's called a die clash, or a "prisoner penny." I'm sure somebody else can explain how it happens, but cool error!
It happens when the hammer die strikes the anvil die when there is no planchet in the chamber. The designs on each of the die transfer to each other. At least that is the short and simple answer at least. Here is a clash from my collection. They are tough to photograph IMO.
Now to answer What's it worth? To start.. 1 Cent.. Collectorwise.. Only what a collector is willing to pay for it. No big premiums for Die Clashes.
