Imagemagick is a image editing program that uses a scripting language to create, edit, and convert many different image formats.
Make Picture Book
This script will take a folder full of JPEGs and make a PDF document out the them where there is one image centered on each page. The page size will have a standard letter ratio at 72 DPI.
magick *.jpg -gravity center -extent 612x792 -density 72 output.pdf
- imagemagick.org/script/index.php - Official.