哪些复制保护技术可用于数字材料？
假设网站为高级用户提供以下资源：
- PDF 文件
- 视频文件
- 演示文稿（例如 .ppt 文件）
可以使用哪些保护技术来防止（减慢）用户复制和重新分发这些资源？
Suppose a website offers the following resources for premium users:
- PDF Files
- Video Files
- Presentations (e.g. .ppt files)
Which protection techniques are available to prevent (slow down) the user to copy and re-distribute these resources?
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PDF - 密码保护
视频文件 - DRM（没有许可证文件无法播放）
演示文稿？不知道。
大多数这些技术也是肯定会阻止普通用户访问您的网站的技术。
PDF - password protection
Video files - DRM (unable to play without license file)
Presentations? No idea.
Most these techniques are also sure techniques to repel normal users from your site.
保护您的资料的一个好方法是使您的网站成为获取/查看/访问您的资料的最简单方法。请注意，苹果公司通过在 iTunes 上销售完全不受保护的 MP3 赚取了数百万美元，因为对于大多数人来说，在 iTunes 上获取它们比在 torrent 网站上找到它们更容易。
最终，您将无法阻止坚定的用户复制和重新分发您的材料。你最多能做的就是尝试减慢它们的速度。无论您最终使用哪种加密方法都需要密钥，并且该密钥最终需要位于您用户的计算机上。因此，坚定的用户将拥有从您那里获取内容所需的一切。你能做的就是让普通用户感到恼火，让他们认为不值得这么麻烦。然而，在烦人的用户足以让他们付费和烦人的程度让他们完全离开你的网站之间有一条微妙的界限。
One good way to protect your material is to make your web site the easiest way to get/view/access your stuff. Note that Apple makes millions of dollars selling MP3's on ITunes that are wholly unprotected, because it is easier for most people to grab them on Itunes than to find them on torrent sites.
Ultimately, you will not be able to prevent a determined user from copying and redistributing your material. The most you can do is try to slow them down. Whatever encryption method you end up using will require a key, and that key will need to end up on your user's computer. Therefore, a determined user will have everything they need to grab the content from you. What you can do is annoy average users enough that they decide it is not worth the trouble. However, there is a fine line to walk between annoying users enough that they pay, and annoying them so much that they leave your site entirely.
没有什么可以阻止用户重新分发可以下载到本地设备的任何内容。也很少有人会真正“放慢”这一速度。大多数都会给合法用户带来完全的不便。
创建引人注目的内容并以令人信服的价格提供。那些看到价值的人会购买它，那些看不到价值的人永远不会开始购买它，所以你真的会失去任何东西。
Nothing will prevent the user redistributing anything that can be downloaded to the local device. Very few will actually 'slow down' this either. Most all will inconvenience legitimate users completely.
Create compelling content and offer it for a compelling price. Those that see the value will buy it, those that don't see the value would never buy it to begin will so you are really losing anything.
对于图像，您可以添加水印（图像上的半透明文本，但不是很明显，例如“© 2010 Me inc.”）。
视频文件也是如此，但在视频中，您可以移动它以使删除它的过程（这已经非常困难）变得更加困难。
演示文稿，我也不知道，但你总是可以尝试使用“© 2010 Me inc.”。在所有幻灯片的底部，或在背景图片上。
事实上，没有办法完全保护您的文件，但这些解决方案将尽力减慢速度，并可能阻止用户重新分发您的工作。
For images, you can put in a watermark (translucent text over the image, but not very noticible, saying something like "© 2010 Me inc.").
Same goes for video files, but in video you could move it to make the process of removing it (which is already extremely hard) harder.
Presentations, I have no clue either, but you could always try having "© 2010 Me inc." at the bottom of all the slides, or on the BG picture.
In truth, there is no way to fully protect your files, but these solutions will do the best to slow down, and possibly stop the user from redistributing your work.