This takes a bit of attention to detail but is very effective.
The key feature we are exploring is the layer styles. They allow us to remove
portions of an image and retain the styles treatment at the edges. Thus with the spattered blood in this case has highlight and shadows appropriate to it's placement. If there is sufficient interest I can post a package of the Photoshop file for this tutorial and a page of spatters that you can use to make your own spatter brushes. OOPs, then I will have to do a brush making tutorial. Oh well, so it goes.