Thank you for the article, it is very informative and has inspired me to implement something very similar.
You mention in the article that you do not want to share your Flickr API key with the world, but is this not exactly what you will be doing by using it in a JavaScript program? Surely this is freely available to anyone who visits your site, since the JavaScript needs to be downloaded and executed by the browser?
Would it be better to have all the business logic implemented server side rather than client side? (forgive me if I have missed something)