There are different ways in proceeded with an authentication of the diploma(this is from U.S. based experience):
a) You may go to the registrar’s office and request a notarized degree issued to you. Usually Universities have a notary on hand or have a notary come with you and witness dean signing the degree. OR
b) Notarize the copy of the diploma with an affidavit
Both ways maybe accepted, however, it is best to verify with the target authorities which one suits them best. Some countries require the diploma to be brought in for accreditation into respective authority designated by the target country this is done to avoid misuses of the legalization process by the diploma mills.
The Apostlle which is a separate page affixed to the document authenticates the document in accordance to the Hague Convention of 1961. Not all countries accept apostille thus it is best to check the list of the countries that signed the convention or consult someone competent on the issue. In any case, without an apostille any document has no validity outside the country of its origin. Furthermore, apostille only authenticates the documents intended to be use d abroad. There is no purpose of getting an apostille if you plan to use the document in the same country the document was issued.
Here’s a link about Authentication of Academic Creentials: http://apostille.us/Documents/authentication_academic_credentials_for_abroad.shtml
Hope this helps.