Due to laws of optics, when a subject such as an outstretched arm or leg occupies both the foreground and the background of a scene captured on camera, it will appear elongated and thus distorted. The shallower the depth of field, the more pronounced the effect will be. With every exposure, the camera lens transposes the three-dimensional world onto a two-dimensional plane. This flattening can skew the relative proportions of objects in much the same way that a two dimensional map of the world exaggerates the sizes of the landmasses at either pole.
