An authentic autograph is when the celebrity actually signs the photo, index card, etc. You can tell when autographs are authentic usually because they are different.
A Pre-Print or facsimile is when the celebrity signs a photo; then that photo is photocopied and those photocopies are sent to fans when an autograph is requested. Pre-Prints are among the easiest "fakes" to recognize because every single autograph is identical.
JC
cernan@fanmail.biz Feel Free to PM or Email me with any questions or comments! I will try to answer as soon as possible although that may not always be possible due to my busy schedule.