From The Art and Popular Culture Encyclopedia
Mistaken identity is a defense in criminal law which claims the actual innocence of the criminal defendant, and attempts to undermine evidence of guilt by asserting that any eyewitness to the crime incorrectly thought that they saw the defendant, when in fact the person seen by the witness was someone else. The defendant may question both the memory of the witness (suggesting, for example, that the identification is the result of a false memory), and the perception of the witness (suggesting, for example, that the witness had poor eyesight, or that the crime occurred in a poorly lit place).
Because the prosecution in a criminal case must prove the guilt of the accused beyond a reasonable doubt, the defendant must convince the jury that there is reasonable doubt about whether the witness actually saw what the witness claims to have seen, or recalls having seen. Although scientific studies have shown that mistaken identity is a common phenomenon, jurors give very strong credence to eyewitness testimony, particularly where the eyewitness is resolute in believing that their identification of the defendant was correct.