You can also search for previously uploaded photos and add them to your new photo album. This approach might be useful, for example, when preparing a "Year in Review" type of album.
Note: When a photo is uploaded to an album, the system creates four sizes of the photo for display purposes: a Thumbnail, plus Small, Medium, and Large images. The photo is stored in the Image Library and you can edit the various sizes there, if necessary (and use the photo on other Web pages). However, only JPEG images that have been specifically uploaded through the Photo Album application can be used in photo albums because of the need for these various sizes of each image.