An embodiment provides a watermarking method comprising the steps of: receiving first image data as input; detecting an insertion region from the first image data; and inserting a watermark corresponding to user information into the insertion region, and synthesizing the inserted watermark with the first image data, wherein the step of detecting the insertion region comprises the steps of: detecting a first region having frequencies in a first range from the first image data; generating a virtual code applied to the first region; generating second image data by synthesizing the virtual code with the first image data; and detecting a second region by comparing the second image data with the first image data, and extracting the second region as the insertion region.