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$photon_removed = remove_filter( 'image_downsize', array( Jetpack_Photon::instance(), 'filter_image_downsize' ) );

// Call wp_get_attachment_image(), wp_get_attachment_image_src(), or anything else that ultimately calls image_downsize()

if ( $photon_removed )
	add_filter( 'image_downsize', array( Jetpack_Photon::instance(), 'filter_image_downsize' ), 10, 3 );