What docidle said.
My tutorial may seem a bit convoluted but my pedantic explanations are meant to be studied just like reading and re-reading instructions until they become very familiar.
Unfortunately there are some differences between my tutorial on posting pictures from Flickr vs. Postimage but the principles involved are quite similar. I suggest you use the testing forum to experiment and practice.
FWIW, here's my Flickr tutorial:
http://cs.finescale.com/fsm/feedback_help_and_testing/f/43/t/173158.aspx