Hi Trevor.
I'm not sure if it is the Witch Head Nebula but if you have a look to the bottom left of Rigel you will see a patch of what I believe to be IC 2118.
It is extremely dim but refering to my planetarium software, it is in the exact spot of the nebula.
I strecthed the image in PS and circled it in red. The only other thing it could/might be is a reflection off the lens.
What do the others think?
It might be worth having a look at the high res version as well.
But like your last image focus and tracking is spot on.
