If you look at it carefully, you'll note that even after deriving the canonical path, they still use the original (unchanged) path as the dictionary key.
It's a fair point that it might be better to use the canonical path as the key - at the very least, it would catch cases where the user passes in both the unix-style and windows-style paths at different times. That said, calculating the canonical path isn't free, so you might prefer to keep the current version, which is very fast in the already-loaded case.
When would I need to use the same image again? I am a newbie in games so don't know when that might be required.
