For the goods listed on the website of the Korean customs service, an import declaration is exempted; when they are exempted from Customs duties or when their duty rate is 0%. A copy of B/L could be filed as a substitute.
However, if any of those items have any commercial value, an import declaration needs to be made;
-Diplomatic goods that are Customs-duty exempted,
-Goods brought in by a visiting foreign President, his/her accompanied family member and staff
-Dead bodies or bones
-Goods used for media such as films and record tapes that contain newspaper articles or news
-Documents produced by overseas Korean consulates to the Ministry of Foreign Affairs and Trade
-Historic documents and paper