docs: def ui_iiif_image_url(obj, version='v2', region='full', size='full',
                        rotation=0, quality='default', image_format='png'):
      """Generate IIIF image URL from the UI application."""
      return u'{prefix}{version}/{identifier}/{region}/{size}/{rotation}/' \
          u'{quality}.{image_format}'.format(
              prefix=current_app.config['IIIF_UI_URL'],
              version=version,
              identifier=quote(
                  iiif_image_key(obj).encode('utf8'), safe=':'),
              region=region,
              size=size,
              rotation=rotation,
              quality=quality,
              image_format=image_format,
          )