From INS website....
How Do I Know If I Need Original Documents?
Applications and Petitions must be submitted in the original.
The INS requires documentation to prove the existence of relationships and facts in support of petitions and applications. The following will clarify when originals are required and when photocopies may be submitted.
Submission of Supporting Documents - Original vs. Photocopy - If a supporting document is prepared by the issuing authority solely for the purpose of presentation to INS, an applicant or petitioner must submit the original document with the application or petition. Examples of supporting documents which must be presented in the original are:
Form I-20 issued by a Designated School Official to a foreign student
Form IAP-66 issued by a Program Officer to an Exchange Visitor
Labor Certification issued by the Department of Labor
Labor Condition Agreement with the Department of Labor endorsement
Form I-693 Medical Examination issued by a authorized civil surgeon
Vaccination Sign-off Supplement to Medical Examination Certificate
Attestations, formal consultations and advisory opinions (e.g., a letter from a recognized expert attesting to someone’s extraordinary professional skills)
Affidavits prepared in place of unavailable documents (e.g., an affidavit in place of a birth certificate where the official records were destroyed by fire)
Translations of documents (even when the rules allow submission of a photocopy of the document itself.)
NOTE: If the applicant or petitioner has already submitted the original document to INS in connection with another matter, he or she may submit a photocopy along with an explanation of when and why the original was previously sent to INS.
For all other documents, the applicant may submit a photocopy of the document required; however, he or she may be required to present the original:
in person, upon the request of an INS or consular official during an interview, or
by mail, in response to a written request from INS.
An original document submitted under these circumstances will be returned to the petitioner or applicant when no longer required.
NOTE: Although the law prohibits duplication of naturalization certificates, certificates of citizenship, and Permanent Resident Cards (formerly known as Alien Registration Cards and commonly called “Green Cards”) for some purposes, that prohibition does not apply to making a photocopy for submission to INS in conjunction with an application or petition.
NOTE: Original documents submitted when not required will remain a part of the record. If you decided at a later time that you want your original returned, please file Form G-884 with the office where you submitted the original document(s). The Form G-884 is available for those in the U.S. through Forms by Mail.
Regulations: 8 CFR 103.2(b)(4); 8 CFR 204.1(f).