Sometimes the situation arises that you hand your iPad to a friend to let them look at a photo collection, but there are some photos in it that you'd rather not share. Instead of deleting them, iOS 8 allows you to simply hide them. Hiding a photo will take it out of the "Years" and "Moments" collections and will put it into an album dubbed "Hidden."
To do this simply open the photo in question then tap and hold. An option to Copy or Hide will pop up, tap on Hide. The photo will be moved to your Hidden album. If you want to "Unhide" it, go to the photo in the Hidden album and do the same thing. Now the options will be Copy and Unhide.