Photo Sharing from iTunes
Mathias is correct about the proper way to sync photos to your iPad. Sharing photos from iTunes approves them for Home Sharing, a system designed to share iTunes Store purchases and media amongst family members.

Apple Knowledgebase: iTunes: Setting up Home Sharing on your computer

Home Sharing can also be used to allow access to photos from an AppleTV.

Apple Knowledgebase: Setting up Home Sharing for Apple TV (2nd generation)