1945-D Lincoln

Fixed I think

More specific than Machine Doubling (which this actually is not) would be Die Deterioration Doubling. As the die ages, parts of the outer edges of the devices near the rim chip away leaving cavities int he die that allow more metal to strike up into them. The effect is a shadow-like hump to the outside of these areas. that's what you are seeing on this coin. It is especially common on some years of cents, but the 1955 got all the fanfare because people were finding them back when the craze started about the 1955 doubled die and thought they had just won the lottery. Unfortunately they were mistaken, as are people who buy these at a premium still. They are exceedingly common and are not worth any premium value at all.