An image processing device 10 includes: a segmentation unit 21 that segments an input image 200 representing a result of observing an ocean surface region and a land surface region from overhead into ocean surface block images 211 and land surface block images 212, based on a segmentation criterion 210; a first determination unit 22 that determines a binarization criterion 220 for the ocean surface block images 211, based on a scattering model for electromagnetic waves in the ocean surface region; a second determination unit 23 that determines a binarization criterion 230 for the land surface block images 212, based on the binarization criterion 220 and a positional relationship between the ocean surface block images and the land surface block images; and a generation unit 25 that generates a land mask image 250 by performing binarization processing on the input image 200 based on the binarization criterion 220 and the binarization criterion 230. Consequently, the image processing device 10 improves the accuracy in generating the land mask image for differentiating between the ocean surface region and the land surface region in remote sensing technology.