A gaming machine and game coupons are disclosed for allowing an operator to redeem winning game coupons by inserting them directly into the gaming machine rather than by taking them to a cashier. The game coupons are coded with a machine-readable prize code which represents a number of prize game credits. The gaming machine includes a bill validator for accepting currency and winning game coupons from an operator. It also includes a code reader for reading the coupon prize codes as the coupons are inserted into the bill validator. The gaming machine issues game credits to the player depending on the prize codes of the submitted game coupons. The gaming machine also incorporates a fraud prevention scheme to guard against fraudulently copied or duplicated winning coupons. Each winning coupon is coded with a unique coupon identification code. The code reader reads and records the coupon identification code of each winning coupon as it is submitted. Subsequently, as further game coupons are submitted their coupon identification codes are checked against the codes already recorded. Detected duplicates are rejected.