What this coin looks like (obverse, reverse, mint mark location, special features, etc.):
One major error is the 1943 DDO (Doubled Die Obverse) Washington Quarter from the Philadelphia Mint. The best way to identify this coin is to note the prominent doubling of the letters in the words "LIBERTY" and "IN GOD WE TRUST". In addition: The 1943 date is also slightly doubled as depicted in the example image above. Coins with a stronger and more noticeable doubling are worth more.
Coin valuation chart: Typical coin prices, values and worth per grade or condition - in USD