Check your Photo sync settings in iTunes on the iPad. The iPad must be plugged in and selected (or set up to sync via wi-fi and selected).
In the Photo sync settings, make sure the correct folder is selected. If you have by album/folder sync option selected make sure the folder you are editing is selected.
Hold in mind that only one level of folders will sync with the iPad. You have a main folder you select to sync. All the top level folders in that folder will become albums on the iPad. You can't have folders inside the album folders. They will be ignored.
Also make sure that the image files are standard jpg, png, or tif files. I think there are a couple more formats supported, but don't get crazy.
After you check all that, try syncing again.
Good luck.
Ref:
http://support.apple.com/kb/HT4236?viewlocale=en_US&locale=en_US
