How the pages are laid out
On A4 or Letter pages, each image is scaled to fit inside the page and centered, with a white margin around it. The large margin is twice as wide as the small one. Ask for “no margin” and the image can reach the edges of the page. A small image is not stretched to fill the page; it is placed in the middle at its printed size: the resolution saved in the file, so a 300 dpi passport photo is 35 × 45 mm, or 72 pixels per inch when the file has none.
With the fit option, every page is exactly the size of its picture, so there is no border and no orientation to choose. This suits screenshots and other images that will mostly be viewed on screen.