If you choose Link to originals in the main jAlbum settings (Album » Settings » Pages), your images will not be scaled or modified in any way. They will be used directly in the slide pages of the album. If you accept the default Gromit setting that makes the pages responsive, Gromit will adjust the slide display to the visitor's viewport, but because the files have not been scaled, the file sizes may be very large, making this setting a poor choice for a web album. However, you can resize your images before using them in jAlbum, in which case choosing Link to originals would be suitable.
Even if you choose to Link to originals, Gromit uses the image bounds entered under Album » Settings » Images » Image bounds » Images to determine the layout of the page title and its navigation icons, and to set size limits for the video player window. Therefore, even if you choose to Link to originals, you should choose suitable image bounds, matching the actual maximum dimensions of the bulk of your images.