Disk copy is a way to make an exact same copy of the original hard drive, and this copy can be used directly. However, disk image is more like creating s large .zip file, with all data compressed in it. Disk image cannot be used directly, unless you make a restore.
So what are their differences?
According to what we have said from the start, we can draw the following conclusion:
Advantages of disk copy:
Disk copy requires more disk space than disk image;
Disk copy can be used as soon as it is finished;