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If you check in the "Guides' section, and look in 'Case Dimensions' a standard DVD cover should be: 10.75" X 7.1875"
An easy way to do this is make sure you scan your cover @ 300dpi, use editing software (i.e. photoshop) to clean up any mess on the cover (sticker residue, etc) then crop and edit the size to 3226L x 2156H pixels.
Then Upload.
I coluld not determine what resolution you scanned your cover at, Ifranview did not show how many dpi (it was blank).
Hope this helps,
Again, welcome!