iOS Intercepting HTTP image request & substituting with local image

Question

I'm writing an application that loads one of our websites into a UIWebView. To speed up the loading times I've created sub class of NSURLCache which checks a NSDictionary to see if the images exists locally and if so it uses the local image rather than requesting the online version. I have an issue though, some of the images have the same name, but in different folders. Here's my NSDictionary:

[NSDictionary dictionaryWithObjectsAndKeys:

@"1-Stars.png", @"https://www.xxx.com/content/star-bar/1-Star/1-Stars.png",

  @"1-Stars.png", @"https://www.xxx.com/content/star-bar/2-Star/1-Stars.png",
  @"2-Stars.png", @"https://www.xxx.com/content/star-bar/2-Star/2-Stars.png",

  @"1-Stars.png", @"https://www.xxx.com/content/star-bar/3-Star/1-Stars.png",
  @"2-Stars.png", @"https://www.xxx.com/content/star-bar/3-Star/2-Stars.png",
  @"3-Stars.png", @"https://www.xxx.com/content/star-bar/3-Star/3-Stars.png",

  @"1-Stars.png", @"https://www.xxx.com/content/star-bar/4-Star/1-Stars.png",
  @"2-Stars.png", @"https://www.xxx.com/content/star-bar/4-Star/2-Stars.png",
  @"3-Stars.png", @"https://www.xxx.com/content/star-bar/4-Star/3-Stars.png",
  @"4-Stars.png", @"https://www.xxx.com/content/star-bar/4-Star/4-Stars.png",

  @"1-Stars.png", @"https://www.xxx.com/content/star-bar/5-Star/1-Stars.png",
  @"2-Stars.png", @"https://www.xxx.com/content/star-bar/5-Star/2-Stars.png",
  @"3-Stars.png", @"https://www.xxx.com/content/star-bar/5-Star/3-Stars.png",
  @"4-Stars.png", @"https://www.xxx.com/content/star-bar/5-Star/4-Stars.png",
  @"5-Stars.png", @"https://www.xxx.com/content/star-bar/5-Star/5-Stars.png",

 nil];

In may app I have the images in the same folder structure as online, so how do I tell a request for 'https://www.xxx.com/content/star-bar/1-Star/1-Stars.png' to use the correct image and not the image meant for 'https://www.xxx.com/content/star-bar/2-Star/1-Stars.png'?

I hope that's clear!