You can also initially do a quick opinion offered by some of the authentication companies. You e-mail them a scan of what you'd like authenticated and they will give you an opinion as to whether or not the item if submitted would pass.
This is an example of the reply that you would receive:
Likely to be genuine: Our authenticators believe that the item, if physically submitted to P.A.A.S. for examination, would likely receive our certificate of authenticity.
Thank you for your trust in P.A.A.S.
Michael Frost
Here are some companies that do the quick opinion for about $10.
Professional Autograph Authentication Services
www.autographcertificationexperts.com - Home
PSA/DNA Sports Authentication Services