The first Amiga (A1000) was put together so fast that the basic operating system couldn't be supplied in the system ROM.
Instead it had to be loaded via floppy disk and then a normal system could be booted.
The image itself is stored as a list of drawing commands, because it used up less precious ROM space. Later versions looked slightly different, because the commands were slightly optimized to save even more space.
Necronom created a small AMOS tool to paint the image from the ROM data and make this process visible.
The disk is shown being held with the left hand which is actually a bit strange, because the Amiga's disk drive is on the right side of the case, so you would usually have to insert it with your right hand.
Sheryl Knowles stated in an interview that she created that image by holding a disk in her left hand for reference while creating the drawing.