A common way to tell if a print is a hand lithograph or an offset lithograph is to look at the print under magnification. Marks from a hand lithograph will show a random dot pattern created by the tooth of the surface drawn on. Inks may lay directly on top of others and it will have a very rich look. Prints from an offset press will show a mechanical dot pattern from the color separations. Each color generates a separate dot pattern that when combined produce a very small circle or "rosette". The dot patterns look like the dot from the newspaper comics but smaller. You can easily see these dots under small magnification or sometimes with the naked eye. All the dots line up in neat little rows. If you can see these dots it is a sure sign of camera and commercial involvement. If the dots are random and you purchased the print from a reputable dealer it is most likely a hand drawn lithograph.

http://www.stonescrayons.com/litho.html

--------------------------------------------------
Note added at 32 mins (2012-12-02 18:44:54 GMT)
--------------------------------------------------

Photolithographs are made up of a fine pattern of printed dots. These dots are visible under a strong magnifying glass or microscope. For black and white prints the dots are black. For color prints there will be a variety of color dots. Under microscopic magnification, the dots appear like splotches of paint or color glue. Digital computer prints, including giclees, closely resemble half-tone lithographs.

http://www.cycleback.com/photoguide/digi.htm