Pixelates only the regions of an image occupied by detected faces, leaving the rest of the image untouched. Maps to Cloudinary's e_pixelate_faces[:N].

:scale follows the same convention as Ops.Pixelate — smaller values produce coarser blocks. The interpreter delegates to Image.Plug.FaceAware.pixelate_faces/2, which is gated on the optional :image_vision dependency.