I would guess that you created (a bunch of) static GreenfootImages, it definitely looks like it's possible to create those images with the drawLine and fillRect the most complicated image looks the empty squares.
(If you didn't use static images, then you probably could.)
2017/4/30
Base Defense
2017/4/24
TetrisClone
2017/4/14
Stopwatch (relocated)
2017/4/13
MineSweeper
2017/4/10
ChessWorld
2017/4/10
ChessWorld
2017/4/10
ChessWorld
2017/4/10
ChessWorld
2017/4/10
ChessWorld