ESPN uses Shotspot to determine a particular ball landed in or out. For one, i have my reservations about how well they can even predict the trajectory of the ball - accurate enough to make a judgement on the line call? I dont think so.
But all that aside, when a ball lands like this (right of the line being "OUT", they claim that it has actually landed on the line, simply becuase in the top view, it overlaps with the line. Yet, considering that the ball contacts the court only at a tiny area, id say they are wrong and grossly misleading the public about close line calls. I am not a professional, but i have played enough USTA sanctioned tennis games to say that in a game, this ball would most likely be called out simply because you can clearly see daylight between the line and the contact area of the ball with the court (which is really tiny) ... Espn should offer an explanation about their shotspot technology - its really misleading I think!
Shotspot is actually a version of Hawkeye - the one used in cricket, where really the accuracy needed is a lot lesser. maybe some of the cricket gurus can throw light on this one ...