Webster's Revised Unabridged Dictionary · 1913

microphotograph

microphotograph (mī`kro*fō"to*grȧf or mik`ro*fō"to*grȧf) , noun

[Micro- + photograph.]

1.
A microscopically small photograph of a picture, writing, printed page, etc.
2.
An enlarged representation of a microscopic object, produced by throwing upon a sensitive plate the magnified image of an object formed by a microscope or other suitable combination of lenses.

A picture of this kind is preferably called a photomicrograph.