The Collaborative International Dictionary of English v.0.48:

Micrograph \Mi"cro*graph\, n. [See Micrography.]
   1. An instrument for executing minute writing or engraving.
      [1913 Webster]

   2. a graphic image, such as a photograph or drawing,
      representing an object as seen with a microscope, usually
      much enlarged as compared with the original object. A
      photograph of a microscopic image is also called a
      photomicrograph or microphotograph.
      [PJC]