Are these pictures on your iPod no longer stored on your PC or in a backup somewhere? If so, you'll need the help of third party software to assist you with the task of extracting the photos from your iPod to your PC. Keep in mind that these synced photos are no longer in their full resolution, but instead are scaled down thumbnails of the original.
If you stored these photos in full resolution, see this article for instructions on copying them from your iPod back to your PC.
Once the photos are on your PC again, you can configure them to sync to your iPhone.