An infamous cheating incident from the 1999 comrades marathon, relevant bits from the Joburg times newspaper report:-
An athelete who admitted cheating by running South Africa's Comrades Marathon, one of the world's most grueling road races, in relay with his look a like brother, was disqualified. One brother ran the first half then the other brother completed the second half, changing in a roadside toilet.
The brothers' plan was only foiled because photographs of the race published in Beeld, Johannesburg's daily newspaper, showed runner number 13018 at one stage wearing a yellow watch on his left wrist. At another stage the runner with that number was wearing a pink watch on his right wrist.