Hi
it looks like the second shutter curtain is sticking. The shutter has a rubber buffer/block in it, and I'd say it has aged, and has started to disintergrate. This is causing the shutter blade to stick open, causing a band on your pics.
Only way to fix it is to fully strip the shutter and replace the rubber block - which even when I was doing them on a regular basis is a good 3 hour job..
Having said that if the camera is in good overall condition it would be worth doing, as the same thing could happen to the next one you buy..
And before you ask - this is a common thing with all EOS cameras, so always check for traces of black stuff/gunk on the shutter blades when buying a camera..
Cheers