Where does magento store its cached images?

I know that magento resizes the original product images and caches it multiple times with different sizes according to its need. - Where are those chached images stored (path)? - Are they the ones that will get deleted when you flush image cache from cache management? - If I were to manually cache some images, where would I have to put them in order for them to get deleted when you clear cache from cache management? Thanks :)