Enter the following codes at the 'Password' screen, a message will confirm if they have been entered correctly.
Unlock Bird's Nest Costume:
Lilly, Lilly, Lilly, Lilly
Unlock Ship Costume:
Frogger, Frogger, Frogger, Frogger
Unlock Hidden Image 1:
Frogger, Frogger, Frogger, Frogger
Unlock Hidden Image 2:
Finnius, Finnius, Finnius, Finnius
Unlock Hidden Image 3
Berry, Berry, Berry, Berry
Unlock Hidden Image 4:
Dr Wani, Dr Wani, Dr Wani, Dr Wani