Apostille is a certificate attached with the original certificate. All the authentication process is done on this ceperate Apostille sheet. It shows that the certificate is geniuine. And the person who signed in the document is the Authorized person of the Organization.
In 1961, some countries agreed to be the member of the Hague convention.

The signed countries are following the method of Apostille. And the other countries are still using the normal method of legalizing the document. Those are the members of Hague convention

Member countries of the Hague Convention are:

Albania, Andorra, Antigua and Barbuda, Argentina, Armenia, Australia, Austria, Azerbaijan, Bahamas, Barbados, Belarus, Belgium, Belize, Bosnia and Herzegovina, Botswana, Brunei Darussalam, Bulgaria, China (Macau), China (Hong Kong), Colombia, Cook Islands, Croatia, Cyprus, Czech Republic, Denmark, Dominica, Ecuador, El Salvador, Estonia, Fiji, Finland, France, Georgia, Germany, Greece, Grenada, Honduras, Hungary, Iceland, India, Ireland, Israel, Italy, Japan, Kazakhstan, Korea, Republic of, Latvia, Lesotho, Liberia, Liechtenstein, Lithuania, Luxembourg, Malawi, Malta, Marshall Islands, Mauritius, Mexico, Moldova, Republic of, Monaco, Namibia, Netherlands, New Zealand, Niue, Norway, Panama, Poland, Portugal, Romania, Russia, Saint Kitts and Nevis, Saint Lucia, Saint Vincent and the Grenadines, Samoa, San Marino, Serbia and Montenegro, Seychelles, Slovakia, Slovenia, South Africa, Spain, Suriname, Swaziland, Sweden, Switzerland, FYR of Macedonia, Tonga, Trinidad and Tobago, Turkey, Ukraine, United Kingdom (U.K.), United States of America, Venezuela.