To avoid unacceptable image distortion, I'd suggest either beginning with an image that's close to a multiple of 40x50, or else cropping it to approximately those relative dimensions, before you use that online tool to create a 40x50 image.
(hide) Tired of placing boats or Espionage pieces at the begining of the game? You can go to Game Editors and save some of your favourite positions for future use. (pauloaguia) (show all tips)