When part of the image is unsharp as a stylistic effect, or the emulation of "realistic" effects, such as looking through certain materials, in-image photographs that are blurry, etc.
Do not confuse
depth_of_field, which is a realistic effect of lenses related to focus.
motion_blur, which is a realistic effect of shutters and similar created by fast movement of an object.
bad quality scans, photographs, etc. (which should generally not be uploaded)
