No poster, whether a stone lithograph, or offset lithograph, is the actual "original painting or goauche", that the image is taken from, but a 'route' to produce a reproduction of the original image in quantity.

Is a lithograph the same as a poster?

Typically, posters are digitally printed in bulk.

On the other hand, lithographs are works of art that are hand-printed by an artist (or artisan) that has been reproduced in small quantities from an original image, using grease, ink, water, and a special surface such as limestone.

How can you tell a lithograph from a poster?

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.