Old 50-Baht plastic note - Front
The plastic 50-Baht note was first introduced to coincide with the 50th anniversary of the king's ascension to the throne. The design is light blue fading into ocher in the middle.
Old 50-Baht plastic note - Back
The building on the back of the old plastic note is the Ananta Samakorn throne hall.
Older 50 Baht paper note - Front
Before plastic, there was a paper 50-Baht note. It was never popular - even today the 50-Baht note is the least common bill you'll find.
You'll note that the back of the old paper note was almost exactly the same as the plastic note which replaced it.