code: public String getMimeType() {
  		if (format != null) {
  			if (format == Format.JPEG && progressive)
  			{
  				return "image/pjpeg";
  			}
  			return format.getMimeType();
  		} else {
  			return null;
  		}
  	}
docs: If {@link #check()} was successful, returns a String with the
  MIME type of the format.
  @return MIME type, e.g. <code>image/jpeg</code>