‘But he perceived their craftiness, and said to them, “Show me a denarius. Whose image and superscription has it?” And they said, “Caesar's.” '
Jesus, however, saw through them immediately. And so He called for them to produce a denarius, the silver coin in which the tax would be paid, which bore on it the head of the reigning Caesar at the time that the coin was minted, and what was actually a blasphemous superscription describing him.. Countries who were under Rome could at the time produce their own bronze coinage, but their silver coinage had to be that issued by Rome. This was partly because it was then an indication to the peoples involved that they were subject to the overall control of Caesar and the Empire. The use of Caesar's coin demonstrated the allegiance that they owed to Caesar.
Having that in mind, as soon as they produced a denarius (having the value of a day's wage to a working man) He asked them whose image and details were on the coin. Their reply could only be, ‘Caesar's'.