Buy Sonic's pictures.
Buy Amy's pictures.
Buy Knuckles's pictures.
Buy Tails's pictures.
Put Sonic Shuffle's GD-ROM into your computer to find some hidden artwork.
Set your Dreamcast's date to December 24 of any year. When you play, instead of Lumina you will see Nights.
Like the Nights secret, set your date to April Fool's Day, April 1 of any year.
Complete the game and it will be in Sonic's room. It lets you change some settings.
Buy the first picture of the section "Another" in the album. This let's you play the mini-games you unlocked.
Win the versus mode to win a doll for the character you used to win.