There is no procedure for doing that, using iTunes. When you synced the photos to the iPod, iTunes reduced the resolution of the images to optimize them for the iPod's small screen (and save storage space used by the photos on the iPod). Therefore, they are probably very low res compared to the original photos. The image data is also consolidated into a single database file.
There may be third-party utilities that can extract those images from the iPod.
The only exception is IF you had a setting enabled when you synced the photos to the iPod. On the iPod's Photos screen in iTunes (where you set up syncing for photos), there is a checkbox for Include full-resolution photos. If that was checked when you synced the photos to the iPod, iTunes separately puts a copy of the original image files on the iPod, in a folder called Photos. You can then Enable disk use on the iPod, and manually copy those image files from the iPod using the Mac's Finder.