When we scan your photos, we create a digital image file (.jpg format) for each photo. These are similar to the digital files created with the modern digital cameras, where a file is written on a memory card for each image captured. We deliver these files on a USB flash memory stick.
A DVD slideshow is a video created from your images. The actual image files will not reside on the DVD, just the video of your images. We choose to burn video on DVD so it will allow you to watch the video in the comfort of your own family room or on any computer that has a DVD drive.
So, a USB flash memory stick is for the file delivery. A DVD is for watching a video of your images on your DVD player (you can use your DVD remote to pause your playback at any time).