A tensor of shape (num_images, num_rows, num_columns, num_channels) (NHWC),
or (num_images, num_channels, num_rows, num_columns) (NCHW), or
(num_rows, num_columns, num_channels) (HWC), or (num_channels, num_rows, num_columns) (CHW),
or (num_rows, num_columns) (HW). The rank must be statically known (the shape is
not TensorShape(None)).