An Example of Stamps Cut from Catalogs
C13-15 Graf Zeppelins and Others
One of the ways of faking stamps on the internet is to use color catalogs or illustrations from auction catalogs.

A seller was queried by a potential purchaser who requested a scan of the stamps being offered in a particular Graf Zeppelin lot having all three stamps.

The picture which was sent was (the file is nearly a megabyte so it is a slow loader):
 

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Examine the outlines of the stamps carefully.  They have been cut out of the illustrations in some auction catalog or possibly even some catalog like the ones the Post Office sells.  Careful examination will show that there is a white strip around the edges of the stamps outside the perforations which shows the edge where the stamp illustrations were cut from the source.  (Also take note that the other stamps also show this situation --  not to mention the color differences between them and authentic stamps attributed to the printing .)