What this coin looks like (obverse, reverse, mint mark location, special features, etc.): One major error in the Flying Eagle Cent (Penny) series is the 1858/7 8 Over 7 Overdate error where the 1858 date was stamped on top of the 1857 date. There are a number of things to look for on the obverse of the penny while identifying this coin. The first is to notice that the tip of the eagle is broken up slightly as depicted by the arrow on the left side of the example image above. The next thing to look at is the 1858 date for traces of the "7" under the leading "8". Sometimes this is very hard to spot with worn coins. One last clue is to look directly above the date for an obverse "die chip" which is basically just a very small chip that appears in the same spot on all of these types of error coins. This is depicted by the arrows on the right side of the example image above. Source of example image is courtesy of Heritage Auctions.
Coin valuation chart: Typical coin prices, values and worth per grade or condition - in USD