We have used atomic force microscopy (AFM) to image liquid droplets on solid substrates. The technique is applied to determine the contact line tension. Compared to conventional optical contact angle measurements, the AFM extends the range of accessible drop sizes by three orders of magnitude. We analyze the global shape of the droplets and the local profiles in the vicinity of the contact line. These two approaches show that the optical measurement overestimates the line tension by approximately four orders of magnitude.