Firebug simplifies programming with JSON
The Developer Tools (F12 keyboard shortcut) of popular browsers show the JSON output returned by an API, like this -
Firefox add-on Firebug's JSON tab within the Net tab, presents it neatly like this -
This makes it easy to extract the specific details that you are after.
The above view helps to visualize how to get to a flickr photo's id on making a call using the jQuery getJSON method to one of the flickr API services - data.photos.photo[i].id