All retake portrait images should be the same size as all original portrait images: at least 640×800 pixels and can be JPG, TIF, or PNG. While JPG or PNG are recommended for file size reasons, TIF will work as well. Images above 640×800 pixels (2.133 inches wide by 2.667 inches high at 300 DPI) do not pose any necessary problems, but will take longer to transfer due to their larger file size.
If portrait images are greater than 640×800 pixels in size, they can be flowed onto the page but they must contain the same aspect ratio as 640×800. The aspect ratio of an image can be calculated by dividing the width of the image by its height. For example, 640 divided by 800 is .8.