How can you tell a fake poster, calendar or other old artwork?

        
Real lithograph                                          Reproduction

Pixels, pixels, pixels.

First, you need a good magnifying glass. Look at your poster with this glass, preferably at a solid color like red or black. You should see no printing pixels. Just solid ink.  This is the indication that it is a lithograph. No pixels. Practice this technique by comparing known real lithographs in your collection and a reproduction from your collection. You will see the difference immediately.

Original lithography should never be confused with "Offset Lithographic Reproductions" which are simply copies of existing lithograph artwork. Some smart artists sign and number them and call them "Limited Editions", but these prints have absolutely nothing in common with the fine and skilful art of making an original lithograph. You don't need to be a professional to see the difference. Most "offset lithographs" are made up of thousands of tiny dots (pixels), easily seen by looking through a magnifying glass, and only 4 colors are used: red, blue, yellow and black. Original Lithographs are made of solid colors.

more.....originals

When prints are made using offset lithography, an original (painting, drawing, watercolor etc.) are taken to a commercial printer. The printer photographs the original and then converts all the colors into a combination of 4. (Red, Yellow, Blue, and Black) A negative is made for each of these colors and a photographic plate is prepared for printing. They are run, usually all at once on large high speed presses. The mark of the artist is lost in the translation from original to photograph and then color separation. Depending on the printer, colors can vary drastically from the original.

A common way to tell if a print is a hand lithograph (like old posters and calendars) or an offset lithograph (modern reproductions) is to look at the print under magnification. Marks from a real 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 and solid 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.