Example for caching images by key

[apwelsh]

It appears that it is possible to commit computed images to the cache, but to receive them back from the cache, seems flawed. It seems like I need to already have the computed image before I try to retrieve the image from the cache. (so that it can save it to the cache, which is backward).
So, can you provide a simple example, how I would retrieve a cached raw UIImage into a UIImageView, and if not found in cache call my render function to computer the new UIImage, and save returned image to cache?