How do you import the ScrollWorld and GifImage classes?
The GifImage class can be imported by using the menubar with "Edit>Import class...", selecting the class and clicking the "Import" button. For classes that are not listed there, you will need to download a scenario that contains it. After opening said scenario, you can close it right back up. Then use your windows explorer to select the "ScrollWorld.JAVA" class from that projects scenario folder and copy/paste it into the 'Greenfoot/lib/greenfoot/common' folder. Then it will also be available to import the same way as the GifImage class is.