There are many ways...
Hari_Om -
There are many ways for USCIS to determine if your friend's relative overstayed the visa.
1) I-94 "Arrival & Departure Record" - your friend's relative would probably had to surrender the stub upon checking in at the airport. This is stamped by Immigration Inspector at the port of entry upon arrival, and he/she would write the type of visa and how long the person is allowed to stay. This is one way for USCIS to track.
2) US VISIT System - your friend's relative had most likely had his/her fingerprint and picture taken by the Immigration Inspector upon arrival. This information is digitally stored in USCIS computer and am sure it also tracks when he/she was admitted to the U.S. and under what visa classification. Although I am not positive, I am pretty sure that the data can be accessed by those, who would review your friend's relative's file if he/she were to renew the visa or reapply for admission at the port of entry
He/she can definitely take a risk and try to enter the U.S. again but I got to say, the odds are stacked up against him/her.
Japanese