I used an approach similar to Chris. I duplicated the background layer and using Apply Image, applied the Red channel in Lighter Color Mode masked through the Green channel inverted but left the opacity at 100%. Then I changed the resulting layers Blend Mode to Luminosity. I then created a new merged layer on top duplicated it and repeated the Apply Image a 2nd time with the same settings as the first time. The result was the color image attached below. The rectangles on the hand were the darker areas I think you referred to as the Blood Stains. I created another merged layer and Difference blended it against the original. As you can see it lightened the skin overal but moreso where the darker stains were. As you can see by the green area, it also affected the lips. So after the 1st Apply Image you need to add a Layer Mask and paint Black over the lips. Copy the layer mask to the final merged layer to restore the lips the 2nd time. (I did not mask for illustrative purposes).