Notes for the Flickr image hosting service:
First open another web browser, and browse to the Flickr image you want to add to batgung.com
How to check if an image can be displayed on batgung.com
Look at the Flickr page, and on the top right near the top you'll see 'Share this'. Click it, and in the pop-up window look for the text 'Grab the HTML'. Click it.
If that expands the box to show 'Copy and paste the code below:', the owner of the photo is willing to share it, and you can go ahead and display it on batgung.com.
Here's an example of a Flickr photo that can be displayed on any website.
If you don't see the 'Grab the HTML' option, or it doesn't show the 'Copy and paste the code below:', the owner hasn't made their photos available for use on other websites. See this example.
All is not lost - in the example above, I wrote a short FlickrMail message to the owner TWE42:
Please can we show a couple of your photos?
We run a website for people interested in Hong Kong's history. Please could we display a couple of your photos?
Your Kai Tak photo will be interesting to readers interested in how it looked: www.batgung.com/node/1821
And the photo of the Gas station in Wanchai shows one of the old ww2 pillboxes (you need to zoom right in to see it - thanks for posting such a good scan) that we've been documenting: www.batgung.com/place-map-search?tid=pillbox
I've enjoyed seeing your photos of Hong Kong. Fingers crossed there are more to come!
And they wrote back giving us permission to use the photos.
Which URL to use
Just use the url from the browser that is showing the Flickr image. eg for the second example above, I pasted the URL http://www.flickr.com/photos/twe42/3422370576/in/set-72157616390298305/ into the Image (external): field on batgung.
Here's what it looks like when it's all finished.