What is tough resources?
Here tough resources are those which can be sniffed out by CooJah but cannot be downloaded by download tools even by Blader. Why the resources can be sniffed but cannot be downloaded. First let's see a URL or a resource:
http://auction.artron.net/getpic.php?type=s&logo=0&picid=art87440708&remote=&hash=1895e770715a27ad9f86af8e2e439130Bx6Dr6odh5jOz1VO+LEmnAlu
This actually is a URL of a image resource. The image is returned by a PHP script. In this URL, some parameters are dynamic. Such as "hash=xxx". It is different when accessed in different time. That is to say this URL can only be used one time. Once it is used by browser, it becomes invalid and cannot be used again by download tools.

How CooJah solve this problem?
Aiming to these kinds of URLs, CooJah provides functionality of downloading tough URLs. If you found that the URLs that CooJah sniffed cannot be downloaded by download tools. Even you used Blader and check the Use Customized Request Header option, the resource still couldn't be downloaded. Then you can try the Tough URL Download function provided by CooJah.
First you need to add the suspicious URL to Tough URL list. After doing this, once CooJah sniffs URLs that match the rules of tough URLs, the request sending out will be blocked. And the URL will be added to result page. And then you download it by Blader or other download tools. On the Tough page view, right click on a URL, select "Download by Blader" command. Please remember to check the Use Customized Request Header and Forbid getting file size before downloading. And for other download tools, they must download the resource in one single part.