A Life Model Decoy (frequently known by the abbreviation LMD) is fictional.
LMDs are identical in every way to the original subject they are replicating. Fingerprints, retina scans, etc all match the original. They were first used to create duplicates of SHIELD director Nick Fury in order to fool enemy agents of HYDRA.
Recently an LMD was used to replace General Thunderbolt Ross when it appeared that Red Hulk killed him (since it was unknown that Ross was actually Red Hulk). One was also used to replicate the deceased Glenn Talbot.