I've answered the question and am running out of new ways to say the same thing so please forgive my cut and paste answer to you.
A digitized image published on the internet can not be analyzed to determine whether or not the original, hard copy is a forgery. The only exception would be if the information on the internet image were demonstrably false. Just the fact that Polarik would attempt such an analysis is a red flag.
If you're interested in a more detailed and technical analysis, here it is.
http://www.hackerfactor.com/blog/index.php?/archives/235-Bad-Science-How-Not-To-Do-Image-Analysis-Part-II.html
That link is two years old (2008) and has been proved wrong.
I have a simple test for you,
first using a laserjet printer create an Obama COLB and scan it and save it as a JPG.
Second using photoshop and a scan of a blank COLB create an Obama COLB and save it as a JPG
check each for file size as well as the artifacts or fuzzy white spots inside the letters
Then compare the file sizes and artifacts to the “original” Obama COLB’s created by The Daily KOS, fight the smears and Fact check first flattened copy and tell us your results.
to date no one that said that Obama’s COLB is the real thing has ever posted their results for this simple test.