The International Driving Permit is a tricky issue. Few people are well-read in domestic laws, not to mention international treaties. Scams are prevalent. Anti-scam campaigns fail to provide explicit legal grounds. Sometimes, the law itself seems to lack clear interpretation.

The Nature of an International Driving Permit.
An International Driving Permit, contrary to what its name suggests, is not a universally valid driver's license. It is based on an international treaty and only valid among contracting parties (nations). There are over 190 nations on the earth and there are many international treaties among these nations concerning the permission to drive motor vehicles. Many of these treaties are regionally based, like among countries in Europe, ASEAN, American Continent, etc.

Customarily, the term "International Driving Permit" refers to a document prescribed in either:
a. Convention on Motor Traffic (Paris, 24 April 1926)
b. Convention on Road Traffic (Geneva, 19 September 1949)
c. Convention on Road Traffic (Vienna, 8 November 1968)
Among these, the 1949 Convention has the largest contracting membership. Thus an International Driving Permit, more often than not, refers to the document based on the 1949 Convention.
The 1968 Convention aimed to improve the 1949 Convention but, the international politics being as it is, not all the contracting parties of the 1949 Convention readily joined the 1968 Convention. The fact that many of the "major" nations have not joined this Convention makes it somewhat obscure and crippled.
The 1926 Convention is still valid today among its contracting parties. Notably, Iraq, Nigeria and Somalia only accept the International Driving Permit based on the 1926 Convention.
The 1949 Convention and the 1968 Convention are almost identical in their contents except some clarifications and additions in the latter. Also, the 1949 International Driving Permit and the 1968 International Driving Permit look almost the same. One major difference between them is that, while the 1949 International Driving Permit is valid for maximum of one year from the date of issue, the 1968 International Driving Permit is valid for maximum of three years from the date of issue.
There is often a confusion, among laymen and law-enforcing officers alike, as to the difference and validity of these two versions of the International Driving Permit. What makes the scene even more complicated is the fact that many nations have a domestic law which validates the International Driving Permit based on the Convention on Road Traffic of which they are not contracting parties. Following are some illustrating cases:

Scam License
Both the 1949 Convention and the 1968 Convention require that a valid International Driving Permit satisfy following two requirements:
1. that it strictly conforms to the format specified in their Annexes (booklet with gray cover pages and white inside pages, by the size of 105mm by 148mm, etc.),
2. that it was issued by
(1949) the competent authority of another Contracting State or subdivision thereof, or by an Association duly empowered by such authority,
(1968) another Contracting Party or subdivision thereof or by an association duly empowered thereto by such other Contracting Party.
Bearing this in mind, it is fairly easy to recognize and identify a scam license.
First of all, all those credit-card sized international driving (driver's) permits (licenses) are scams.
Sometimes a scam license takes the form of a booklet with gray cover pages and white inside pages, with about the size of 105mm by 148mm. In such a case, it requires some examination whether it conforms either to the 1949 Convention or the 1968 Convention. One such scam license, however, is easy to recognize, as it's "valid" for five years!