Mark 12:16

And they brought it
The penny, which was a Roman one, and worth seven pence halfpenny of our money:

and he saith unto them, whose is this image, and superscription;
for it had the head of an emperor upon it, very likely the image of the then reigning emperor Tiberius, and a superscription on it, expressing his name, and perhaps a motto along with it:

and they said unto him, Caesar's;
one of the Roman emperors, Augustus, or Tiberius; most probably the latter; (See Gill on Matthew 22:20), (See Gill on Matthew 22:21).