If the concept of emulation sounds too good to be true - that's probably because it is. Emulators can use a large percentage of your physical computer's resources during operation. Efficient emulation of the Apple on modern machines is really only possible because of the expanding power of computers. Finally, the Amiga uses DiskMasher images. None of these image types are compatible with each other.
Emulators use disk-images for a totally different purpose.
Whereas modern computers use images to transfer physical diskettes electronically, emulators use disk-images because the original media is not compatible with the modern disk drives. Although the diskette media itself is the same, the method used to store data on it is totally different. Unlike the different types of images above, emulator images can be used on any computer. Because any disk-drive can access the information on a diskette in a number of ways. These are the three main types which are standard to most emulators.