Validity of international driving licence
What
International driving license is necessary only if your driving license does not comply with conditions specified in the Convention on Road Traffic (see links below). If you have a permanent or temporary residence permit (exceeding 1 year), you have to replace your driving license with a Czech driving license within 3 months of the issuance of your residence permit even if you possess international driving license. International driving license is supplement document for the national driving license. Therefore, you always need to carry both documents to be permitted to drive.
How
In case, that your driving license does not comply with conditions specified in the Convention on Road Traffic, you need to obtain an international driving license or Czech driving license. International driving license can be issued only by the authorities of the country, which issued your original driving license. Therefore, you need to obtain it in your home country (or country where your driving license has been issued) before going to the Czech Republic.
Where
International driving license can be issued only by the authorities of the country, which issued your original driving license. Information Publication for Foreigners Czech Republic (in English, Ukrainian, Russian, Vietnamese and Mongolian): http://www.mvcr.cz/mvcren/article/information-for-foreigners-in-the-czech-republic.aspx
Praha 7, Czech Republic
Nad Štolou 3
170 34 Praha 7