Prevent Image Copying - Checking The Referring Page
   
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    GraphicsAcademy.com  >  Tutorials  >  Prevent Image Copying  >  Chapter 4

       

     

    How To Prevent Image Copying

    Chapter 4: Checking The Referring Page

    Another idea to prevent copying (or at least make it annoying and bothersome) is to use an anti-leech script to prevent linking to your images.

    Anti-leech scripts are primarily intended to prevent people hot-linking to your images. What they do is only send the image to the user's browser if the image is accessed from a URL (web page or web site) that you specify.

    In principle you can use this to prevent people simply typing in the URL of your images into your browser. For example, if you have an image on your web site called mypicture.jpg a user might be able to see if they visit your web page http://www.yourdomainname.com/yourpage.html but they won't be able to see if they type into their browser (or link to) http://www.yourdomainname.com/mypicture.jpg.

    While anti-leech scripts are great for preventing hot-linking and protecting your site's bandwidth, they are not so good for preventing copying.

    This is because anti-leech scripts rely on the Referring Page field sent by users' web browsers to identify which page the user is accessing your images from. But, sometimes web browsers do not correctly fill out this field and instead leave it blank.
    • If you use an anti-leech script to prevent hot-linking, it works great:

      For example, imagine that 90% of users' browsers fill out the Referring Page correctly, but 10% don't:

      • If you install anti-leech script on your site, you can configure the script to allow browsers with both valid Referring Pages and blank Referring Pages, to see your images. In which case, all users will be able to see the images on your site.

      • However, if some other webmaster hot-links to your images, 90% of his users (with invalid Referring Pages) will not be able to see your images, and only 10% will.

    • If you use an anti-leech script to prevent copying, it isn't nearly so good.

      For example, imagine that 90% of users' browsers fill out the Referring Page correctly, but 10% don't:

      • When the image "thief" wants to retrieve images from your site, he will probably simply type in the images' URLs. In this case the Referring Page from the browser is normally blank, thus to prevent it you'll have to ban access to images from browsers with blank Referring pages.

      • An unwanted side effect of banning access from browsers with blank Referring pages, is that you also have banned 10% of your "legitimate" users from seeing your images. Ouch!

      • In any case, it is possible for a determined image "thief" to use a browser which spoofs a valid Referring Page, and thus copy your images. So at the end of the day, you haven't really protected your images, but you have stopped many "legitimate" users from accessing your site!
    So, in my opinion, I don't recommend using an anti-leech script to prevent copying of your images - the effect on "legitimate" users is just too great. (I do however recommend using anti-leech scripts to prevent hot-linking, but that's a different issue entirely).


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