Hmm - I see what you mean, the real seal is round while Obama's is not. The circle of dots is distinctive while those on Obama's run together and are blurry, same thing going on with the type and outer circle.
Was the same equipment used to make both impressions? Were both images produced by the same scanner, at the same resolution, with the same settings? Are both images the same generation?
Without the answers to those questions, the evidence is meaningless.