Function fz_compressed_image_buffer 

pub unsafe extern "C" fn fz_compressed_image_buffer(
    ctx: *mut fz_context,
    image: *mut fz_image,
) -> *mut fz_compressed_buffer

Retrieve the underlying compressed data for an image.

Returns a pointer to the underlying data buffer for an image,
or NULL if this image is not based upon a compressed data
buffer.

This is not a reference counted structure, so no reference is
returned. Lifespan is limited to that of the image itself.