jAlbum provides an option to produce HiDPI thumbnails and/or HiDPI images, but there is, in fact, no such thing. A JPG is simply a JPG, with certain physical dimensions, expressed in pixels. What jAlbum does is double the image bounds you have chosen, but then tell the skin that the image is half the dimensions it actually is. If you choose image bounds of 800x600, for example, jAlbum produces an image that's 1600x1200 pixels, but it then reports its imageWidth and imageHeight variables as 800 and 600 pixels respectively. Most skins then show that 1600x1200 pixel image in an 800x600 pixel space, which produces a better display on a high-resolution display like a Retina display.
The NoPages skin, however, doesn't produce any web pages, so it never asks the jAlbum core how large the images are. Therefore, these settings are pointless in NoPages. If you want images that are twice the dimensions, simply double the thumbnail and/or image bounds in the main jAlbum settings.