For newer FileMaker developers it's easy to exclaim "Oh, cool, FileMaker takes care of that for me. Look, it reduces the image to fit my container." Coupled with the false assumption that what you see is optimized to the ideal resolution will give you nothing but a SLOW FileMaker solution.
While it's nice to have something taken care of for you, it's not always the most ideal. FileMaker can only anticipate so many situations and conditions and, as a developer, your solution may require far more