Source : Webster's Revised Unabridged Dictionary (1913)

Overexpose \O`ver*ex*pose"\, v. t.
   To expose excessively; specif. (Photog.), to subject (a plate
   or film) too long to the actinic action of the light used in
   producing a picture. -- {O`ver*ex*po"sure}, n.

Source : WordNet®

overexposure
     n 1: the act of exposing film to too much light or for too long a
          time
     2: the act of exposing someone excessively to an influencing
        experience; "an overexposure to violence on televsion"