To bring it back, tap the photo count above the album grid and choose 'Hidden Photos', then select the image and remove the mark of shame by tapping the cross again.
This doesn't delete the file, it merely hides it from view. Or, if you find a dud, tap the cross icon. When you find images that you want to work on, tap the rosette icon at the bottom of the screen to mark them as a Favorite. Tap and hold photos to add them to a group. To sort and get rid of photos, double-tap on one, and iPhoto selects it with similar shots, giving you a larger preview in the main window. Once your images are imported to your iPad they automatically appear in iPhoto. Anything imported via the Camera Connection Kit is placed under the Events tab, labelled by a photo's date. Anything from iTunes takes its Folder name or iPhoto album name as its album title. Any pictures taken on your iPad or iPhone are saved in an album called 'Camera Roll'. On the iPad or iPhone iPhoto (and the default Photos app) arranges your snaps into Albums, Events and Places. If you're syncing with iPhoto you can choose selected albums, Events or Faces to sync. When you sync, files will be updated on both sides.
Here you can sync with iPhoto or a folder on your hard drive, usually Pictures, and copy files into there. To do this, make sure your iPad or iPhone is connected, select it in iTunes, and go to the Photos tab. Your final option for getting photos onto your iPad is to sync via iTunes.