Is there a way to clear the cache used by UIImage class?

Answer taken from Kevin Low comment

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If you can use private APIs (as in an AdHoc only app, for example) use this UIImage method to remove all images from cache

[UIImage _flushSharedImageCache];

There is no way I know of to manually clear this iOS managed cache. In general, this is a red herring. When the os manages something for you, you don't need to worry about it. As long as you are correctly releasing anything you alloc/retain and handling memory warnings appropriately you're doing your part.