<?php
$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 );
}