A digital watermark information detecting device (200, 400) comprising: a dividing unit (260b, 460b) configured to divide image data into a plurality of areas, wherein the image data is projected by a projecting device and is captured by an imaging device, the image data is obtained by embedding watermark information to original image data, the watermark information is represented by a sequence of bits including any of bit "0" and bit "1" and is embedded in the image data as watermark data which temporally changes with a constant period and a constant amplitude to represent bit "0", or bit "1" by a reversed phase of a phase for bit "0", and another image data which is obtained by embedding another watermark information to the original image data is also projected by another projecting device and is captured by the imaging device wherein the projected image data and the projected another image data are partially overlapped, the projecting device and the another projecting device are respectively configured to project the image data and the another image data so that a phase of the watermark data and a phase of the another watermark data are synchronized and at least some of the plurality of areas overlap; an identifying unit (260c, 460c) configured to extract an amplitude of an area among the plurality of areas, to identify other areas which are neighbored, at least one of which neighbors the area, and each have a same amplitude over time as the area, and to identify the area and the identified other areas as a target area for extraction and to identify as overlap areas that are not target areas, the areas having an amplitude equal to twice or zero times the amplitude of said target area; and an extracting unit (260d, 460d) configured to extract the watermark information which is embedded in the target area for extraction. a dividing unit (260b, 460b) configured to divide image data into a plurality of areas, wherein the image data is projected by a projecting device and is captured by an imaging device, the image data is obtained by embedding watermark information to original image data, the watermark information is represented by a sequence of bits including any of bit "0" and bit "1" and is embedded in the image data as watermark data which temporally changes with a constant period and a constant amplitude to represent bit "0", or bit "1" by a reversed phase of a phase for bit "0", and another image data which is obtained by embedding another watermark information to the original image data is also projected by another projecting device and is captured by the imaging device wherein the projected image data and the projected another image data are partially overlapped, the projecting device and the another projecting device are respectively configured to project the image data and the another image data so that a phase of the watermark data and a phase of the another watermark data are synchronized and at least some of the plurality of areas overlap; an identifying unit (260c, 460c) configured to extract an amplitude of an area among the plurality of areas, to identify other areas which are neighbored, at least one of which neighbors the area, and each have a same amplitude over time as the area, and to identify the area and the identified other areas as a target area for extraction and to identify as overlap areas that are not target areas, the areas having an amplitude equal to twice or zero times the amplitude of said target area; and an extracting unit (260d, 460d) configured to extract the watermark information which is embedded in the target area for extraction.