Whenever possible the original documents, questioned and known, should be submitted.
Known samples must be comparable to the questioned material. Document examination is a comparative process and any known standards have to be the same type of writing as the questioned. If the questioned material is hand printed (disconnected letters), the known should also be hand printed. If the questioned is handwritten (connected, cursive), the known material should likewise be handwritten. In short, the known material should contain the same characters and character combinations as the questioned.
The source of the known writing must be provable and it must be admissible in a court of law.