1) images are not required to be exactly 300×300. That is the maximum allowable and the suggested size. My image appears just fine and it is not 300×300.
2) If you’re stuffing bogus info into the duration tag, then why put anything in there at all? You appear to be concerned about having to manually do it each time. Simply omit the tag and it stays at zero. I don’t understand what you’re trying to achieve if you’re not puting legitimate values in the tag.
-KHD