Old Adhesive with a reverse image of another Cent. Not a Mint Error. Coins are minted/struck.. not printed. Paper currency is printed.
A close up pic would be nicer , Is the overstrike raised or embedded into the penny? If it is embedded into the coin then it was most likely someone whom used a vise to press the one coin onto the other, leaving the impression. I am sure there will be some more answers coming . If you can , another picture of the penny in the upright position and close up will be much better to decipher. Dillan
I agree with @paddyman , an adhesive job . Maybe somebody trying to pass it off as an error coin. Dillan
Someone outside of the US Mint stuck 2 pennies together with adhesive. When they pulled them apart the image of the back of the other penny was left on the dried adhesive. That is why CENT looks backwards.