Ghost scratches I always thought were self-inflicted. If you rub yourself with your fingertips in the same line for long enough (like hours, overnight even) the skin raises up and starts to look like a scar. So, like people who grind their teeth in their sleep, it's just a subconcious thing.
But yeah, looking at your photos 8bit, there's no way you could have done that yourself. I'm a good bit chunkier than you and I can't even reach that high up my back. So, erm...
About the shadow people, I also get them, about the size of a big dog, up to man-sized like 8bit says, not cat-sized. They seem to happen more frequently in some places than in others, like in my mum's house where I see them all the time. I was once at a friend's house, having a cuppa with her mum, the kind of crap small talk you have with someone's mum, and sort of saw someone coming out of the next room and standing in the doorway, peering in. I turn to look and there's no one there. Her eyes light up and she asks me, "You just saw someone at the door, didn't you?" I say, "I thought I did, yeah." She laughs a little, "That's George." Apparently she's the only one in the family who can see 'him', her husband and daughter both think she's mad, but she talks to him and everything, says that as long as you pretend not to notice, he'll stand there until you're absolutely certain he's there, she even says "Hi George," to him, but he never says anything back. If she hadn't been saying it with a smile on her face in the middle of the day, it would have been real horror movie stuff. I quizzed her daughter, my mate about it for weeks but she'd never noticed anything weird in the house at all.
There's a wikipedia article on them:
http://en.wikipedia.org/wiki/Shadow_people
If you see them, then the second picture down will send shivers down your spine.
Best thread for ages btw.