as it happened, i had a couple of images i took the very first time i used my digital eos rebel that had a lot of distortion due in this instance to both a wide angle lens and the slope of the terrain and in the instance below, to the wide angle lens and generally bad picture taking.
in this one, i've used the class example as an inspiration and have drawn vertical and horizontal lines to give you an idea of the extent of distortion.
it was fun and more difficult than i expected to get things more or less appropriately lined up and i had to crop the original quite a bit because of the distortions.
ultimately, i also had to result to the warp option to sort it out completely. you can see the result in the next image.