There is a huge difference between what FactCheck has done and what Polarik claims to have done. FactCheck says they asked for access to the document and presents some photos. Polarik claims to have proven forgery through a forensic analysis of images.
Forensic analysis of evidence is a practical science. There are methods and standards involved in science. In order to be taken seriously one must meet those standards.
In this specific example, if one is going to claim that Hawaiian policy is to change the stamp each year and to only use one variation of the stamp each year, then one better have a citation to something that proves that is Hawaiian policy. Looking at a couple of photos doesn't cut it.
"Looking at a couple of photos doesn't cut it" applies as much to Obama/Factcheck photos as it does to the other collection of photographs; -if you want to make that kind of argument.