1) The blood left on the ground has to be a texture/decal. One that is applied to a new layer above the first texture-layer. The question is how to put it there while in run-time. Of course it is possible, the game uses it all the time, but the code is embedded in the engine (afaik).
2) Keep the pictures the right size. Get a program from ed. depot? I use OFP-studio for that, a great program btw.