Some embassies request an Apostille stamp as proof that your document is internationally authentic.
Consider an Apostille stamp as the ultimate seal of legal approval for your document, as it comes from a government body. Apostille stamps are applied for Premier TEFL in the UK at the Foreign and Commonwealth Office.
Having a clear understanding of the significance of the Apostille stamp is vital if you plan to teach in a country which requests documents to be legalized by a government body.
This is the case in China (Z visa), Vietnam and in Saudi Arabia. Here is a list of countries where an Apostille stamp is not needed, as they are a party to the Hague Convention Abolishing the Requirement of Legalisation for Foreign Public Documents.