If I find better quality pictures of the NA version covers may I submit them for review?
sure.
you can always edit or update items with
new info (an un-released game becomes an "officially released" game),
more info (add an image where there is none or fill-in empty barcode, box text, release date, rating, item number, description, etc fields), and/or
better info (clearer & higher-res pics or, if you see incomplete or only partial box text - you can add to it & make it complete, etc).