If you look at the picture here http://www.factcheck.org/UploadedFiles/birth_certificate_5.jpg and specifically the portion of the embossing above and on the crease in the paper, Polachik has not shown how that item can be photoshopped. If you believe it can, than please show how. If you don't know how, then consider the fact Polachik has not shown how, just stated that it is possible.
I think you are confused by the analysis of the other low res scans on smears, Kos and politifacts (sp?). Those were all low res flat scans where it would be rather easy to create a forgery if one wanted to by leaving the rest of the scan alone (including both types of seal) and only altering the text (replace the original name and details with Obama's name and details). Unfortunately that same type of hypothetical forgery is impossible with the factcheck photos.
Specifically, the forgery would have to include all the artifacts seen in the photo (the preprinted hashed paper, the embossing, the rubber stamp) before the photo was taken.
sorry, I meant Polarik, not Polachik