The Collaborative International Dictionary of English v.0.48:

Fog \Fog\, v. t. [imp. & p. p. Fogged; p. pr. & vb. n.
   Fogging.]
   1. To envelop, as with fog; to befog; to overcast; to darken;
      to obscure.
      [1913 Webster]

   2. (Photog.) To render semiopaque or cloudy, as a negative
      film, by exposure to stray light, too long an exposure to
      the developer, etc.
      [Webster 1913 Suppl.]