Jpgs aren't really a pixel format. They are more like the signals your analog TV gets for it's red green and blue guns. You can stretch jpgs up to 120% and they will create new pixels. There is also software built in to antialias when you do. Better yet you can compress them.  If you take your 2048 square image at 72 dots per inch and squeeze it down to fit an 800dpi page you have actually bumped the resolution up to 187 dpi if you squeeze it down to the normal page width of 600 dpi the resolution goes up to 246 dpi. If you printed your 2048 image at native 72dpi resolution you would need a piece of paper 28.444... inches square. Since you are printing the image on a regular piece of paper you are automatically shrinking it and increasing the dpi in the process. If you display the image on your monitor set at 1280 x 1024 and it fits top to bottom the resolution is 144dpi not 72.