I've been meaning to do this for quite some time, and with the big summer wedding season behind me, I've finally had a chance.  
Getting a good print is crucial to achieving a high quality poster.  The true beauty of the poster is created by each person's own unique fingerprint lines.  Unfortunately, if the print I receive is not clearly defined, there is not much I can do except request a new print.  
Here are a few tips:
– Use a blank piece of paper.  If the paper has something on the back, it will probably show through in the scan.  Also, don't use lined notebook style paper!
– Push finger straight down and don't roll it.
– Use any color of ink, but really light colors aren't recommended.  DO NOT use metallic inks (i.e. silver)
– It is important not to press too hard.  It will make it very difficult to get a print with clear lines
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