We are developing an web application that extends the DotNetNuke to meet our requirements, we store lots of images and videos that we want to limit access to.

Now I know that I can set role permissions from within the dotnetnuke to limit the access, but if a user knows the actual path of the image (ex: http://www.site.com/portals/0/images/image.gif) he can download it without any problem.

I've tried to add a web.config file to deny access to anonymous users but for some reason I can still view thos images or videos, and even excel files without any restrictions. So does anyone have any solution for this?

Thank you for the quick reply, but I'm talking about a minimum of 300 GBs of images and videos at least... and will be updated frequently, to do the DB storage for all of this is a suicide. I can't even think of the daily/weekly backups for this xxx-large db once we store everything in it.

So anyone with any other solutions? or do you have anything else in mind?

Not sure if this'll help but... we did something something along those lines. 

Our documents are not stored in the DNN folders.  We wrote a "securedownload" application that writes the content to the webpage without revealing it's source.  Basically, a validated user gets a dynamically generated link to the  "securedownload".  And "securedownload" looks the path up in a database based on keys generated in the link (something like sessionid and a random guid).

The content delivery in our case is very basic (pdf files).  And (as a far as we know) the documents cannot be accessed without permission.