Thanks for your reply stctr. Ok, for testing purposes, this is what I'd like to happen:
1. Click img sprite button
2. AJAX calls an image file from the server (crucial that I can set this dynamically - it cannot just be a part of the project files)
3. Upon AJAX load complete, the so-far-empty sprite named 'imgReturnedData' should load the image called by AJAX (LastData).
For the final app, this will be expanded somewhat:
1. User creates their user content (in this case, it will be a mugshot generator which they can upload their own photo to. Functionality-only version here: http://www.angelserver.in/html5/mugshot_generator/ )
2. Upon completion, their image is uploaded to our database using a filename generated within the app
3. The user might want to share the completed image on Facebook, Twitter etc, so they click on the particular 'share'
4. AJAX makes a call to our database to retrieve the user-generated image
5. AJAX.LastData is used to pinpoint the share function to the particular image URL on our database. i.e. Image: "http://our.server/images/" & AJAX.LastData & ".png"