Are there some tricks I can use to post materials on a website (text, images, video, PowerPoint files, etc.) so that folks can easily view the material, but cannot easily download it?
Generally speaking, if it’s posted to a web site, it’s accessible.
I do websites for a living and this is one of the most asked questions.
The problem is this, yes you can made it hard for people to download things. But and here is the big but, it can always be done.
So the next issue you have to ask yourself is, “Do I want to go to all the trouble of doing this.”
Simply by disabling a right click you can stop most people. Of course you can disable javascript to get around that.
You can use a php script that calls up a pic so you if you right click you get gibberish, but all you do is got to do is go to the page->source and get the jpg.
This stops even more people. Put in a relative URL instead of an absolute URL and that makes it even harder. Because most people don’t know how to reconstruct the URL.
For pics the best defense I’ve seen is to use a hex code generator. you save your pics in Hex code and use a php or perl script which runs the pic through a hex code generator and that will make the gibberish into a viewable pic.
Of course all you have to do is download a free hexcode generator and right click and copy the gibberish and run it through the hex code generator and you get the pic.
And to be honest there is alway a screen capture which is pretty darn close to the jpg file.
I can honestly say that I’ve never been NOT able to catch a pic off a website. Also php and asp and the like I can even get into files and get profiles and data of those who “supposedly” blocked me.
That said, a simple javascript that disables you’re right click will deter 75% of all people. Use relative and not absolute urls and that will kill off another 10%.
The other 15% are gonna work at your site till they get that pic and they will.
Lastly because a browser has got to be able to call up your pics to view, they will store a cache of it and you can get the pic off there too. This is why it’s so hard, in order to allow a browser to read your files you pretty much are giving it to that person as well as the browser.
Heck I even know of a guy who when you stamp a text over your pic, he can go in thru hex mode and remove it. It’s a lot of work but it can be easily done, though very lengthy and tedious to do.
And annoy the hell out of everyone else.
Remember that, in these days of Firefox and Opera browsers, with mouse gestures, any disabling of right-click also fucks up anyone who uses mouse gestures. There are also other context menu items that people might want to use, and disabling right-click messes with them too.
If i’m at a website and i get a pop-up box when i right-click, it’s usually because i’m using a mouse gesture. This shit annoys me so much that i leave the website immediately, never to return.
Disabling right-click is the sign of a shitty website, in my experience.
Best bet for images is to watermark them. It won’t stop them from being stolen but it help you catch them.
Some of the photography websites I’ve visited show the pictures in a Flash animation. On others, the pictures are stitched together from tiles, so you can right-click to save the picture, but you’ll only get 1/15 or so of it.
and
These are all decent solutions, and have the extra advantage of not annoying the hell out of your visitors.
(Well, Flash can be annoying, but that’s generally if it’s used badly or inappropriately.)
Mouse gestures? 
Sound a bit useless or weird when you first read about them, but once you get used to using them, you’ll never go back.
As far as text, if you display it as an image somebody would have to run the image(s) through an OCR program to get the text. Certainly not too hard, but it adds a certain amount of protection.
However, if you display all your text as images then the search engines won’t index the words either. That’s one thing you have to worry about while protecting your content, what will the search engines see and index?