Currency processing systems, coin processing machines, and methods of imaging coins are presented herein. A currency processing system is disclosed which includes a housing with an input area for receiving coins and receptacles for stowing processed coins. A disk-type coin processing unit is coupled to the coin input area and coin receptacles. The coin processing unit includes a rotatable disk for imparting motion to coins, and a sorting head adjacent the rotatable disk with shaped regions for guiding moving coins to exit channels through which the coins are discharged to the coin receptacles. A sensor arrangement mounted adjacent the rotatable disk includes one light emitting device for emitting light onto a coin surface at near-normal incidence. A photodetector senses light reflected off the coin surface and outputs a coin-image signal for processing the coin.