1. An image processing device comprising: an image acquisition unit configured to acquire an image captured by a first imaging device provided in an optical head-mounted display (HMD) for presenting an augmented real-world image observed when a three-dimensional image in a virtual three-dimensional space is projected onto a real-world setting, the first imaging device being configured to visualize an area including a field of view of a user wearing the HMD; and a marker detection unit configured to detect a marker included in the image captured by the first imaging device and acquired by the image acquisition unit, wherein the image acquisition unit also acquires an image captured by a second imaging device having an angle of view that at least partially overlaps an angle of view of the first imaging device, and wherein, if the marker is not captured in the image captured by the first imaging device, the marker detection unit detects the marker in an image captured by the second imaging device.