Most countries determine obligations to pay taxes on foreign-earned income based on residency criteria. Anyone who is working legally in Korea is a Korean resident and receives proof of this in the form of an Alien Registration Card. This card clearly states the dates of your residency in Korea. As it is not possible to be a resident of two countries at the same time, this card alone should be accepted as proof of your non-residency in your country of origin.

The links below provide information from government revenue agencies. If you are still in doubt about your obligations to pay taxes, speak with a local accountant. In practice, I've never heard of anyone who was legally working in Korea being obliged to pay income tax at home. People who work abroad for a year or two contribute enormously to their home countries' economies. They bring new money back home and spend it, and they don't use any social programs or government services while they are abroad.

More information about income taxes:

Canada

The United States

Australia

The U.K.

Ireland

New Zealand