I have a tripod shot of a body on the ground. We forgot to put blood on his face from a spiked club going across it. Is there a way to add realistic looking scrapes in post? I don`t want it noticable that it is post production work, I want it to look like its there, its a medium far shot. A reshoot is not possible.

Get a guinea pig, maybe yourself, get some white clown paint, cover your face, then put the blood marks you want on your face. Take your new footage and key the white out in post, lay the clip over your layer and see how that goes.

you could even get a picture of blood and guts on the web and edit it photoshop and comp it, tracking it in if need be.

we have to add bullet wounds all the time from dud squibs and it works fine.

ideally you'll be painting on video.
if the shot is still this is straight forward.
depends on what you have at your disposal.
i think the new photoshop lets you import frames.
investigate what you have at yout disposal.
i think the new AE allows painting onto video as well.
you might want to emboss the red to give it depth - maybe

These folks have the blood your looking for....

http://www.videocopilot.net/tutorials.html

We forgot to put blood on his face from a spiked club going across it.

You forgot????

If it is a still shot on a tri-pod why not just export one frame, go nuts in photoshop. then add some noise and what not to make it look like video.