As long as you don't have to support IE6 or IE7, the preferred way to send cross-domain messages between an iframe and its parent is to use window.postMessage(...)
.
Since you have the ability to modify the upload service, you should have it invoke something like this:
window.parent.postMessage('photoUpload.complete', 'https://website.com');
(the second parameter can be set to '*'
to allow the iframe to send messages regardless of the containing page's domain, but that's correspondingly less secure - may not be relevant in your case though as no actual data is being sent).
and your site would use something like
if (!window.addEventListener) {
// IE8 support (could also use an addEventListener shim)
window.attachEvent('onmessage', handleMessage);
} else {
window.addEventListener('message', handleMessage, false);
}
function handleMessage(event) {
// check where the message is coming from - may be overkill in your case
if (event.origin==='https://photoupload.org') {
// check event type - again probably not required
if (event.data==='photoUpload.complete') {
// do your thing
}
}
}
And if you want to send messages back from the outer page to the iframe, it's basically the same setup but you send with:
iframe.contentWindow.postMessage(...)
If IE7 or IE6 support is required, postMessage()
is not supported but you could use something like http://easyxdm.net/wp/