I have done several job for the bbc cleaning up houses they have used as sets. There are different formulations of fake blood available and the ease of removal varies. The fake blood that the make up department is different to the blood in the exploding capsules they use for gunshots etc. There are quite a few manufacturers making different types. I have never failed to remove it but some will come off easier than others. A lot of the time the stain can be removed just by pre-spraying with powerburst then extracting. Other times I have used white vinegar or meths.
As Derek has said if you get a white towel ans put the solution on the towel and dab the stain you will see what will work.
Peter Maybury
www.carpetcleanercardiff.com