It doesn' just work like that - there's a lot more to Greenfoot than the "greenfoot" package. I have made a tutorial how to run Greenfoot scenarios in IntelliJ, a widely used Java editor. Maybe that helps you, it will at least give you an idea about how much there is to do. If you are still interested, there are probably ways to run Greenfoot in BlueJ, but it would be quite complicated for sure. Also, Greenfoot actually IS BlueJ under the hood and has the exact same editor, so I don't know what you are trying to achieve here. If you just need a class to represent images, take a look into BufferedImage from the java.awt package. That's what Greenfoot is using internally as well.