The ONLY way to keep people from taking your images displayed online is not to display them online, period.
In order for an image, or literally any part of a website, to be viewed on a user's computer, the code and images (and any other media) is downloaded to their machine. Since it is downloaded to their machine, they have access to every part of it.
The best option to avoid actual theft of images displayed online (not just some guy saying "hey this is nice, I want to use it as a desktop background") is to watermark your images. Look at all of the image vendors out there, they do not make the full high rez versions without watermarks available until you purchase them, otherwise there is always a ghost image of their logo over their products.
Anything less is EASILY defeated.
here my "two cents" and some voices from other persons stored in my library:
If you really want to try it, here my draft: http://hansgd.de/AdobTest/alertBox/alertBox.php. I'll give you here the link to a German website (no problem to adapt the source code) where you can create an alert box (BUT I remember David Powers "substantiation of opposition" to it): http://www.6webmaster.com/homepagetools/klicksperre/do.php
Rechte Maustaste sperren Generator > (der Albertbox-Text erscheint bei Rechtsklick eines Besuchers) > Gewünschter Text für Alertbox:
means something like:
Right Mouse Button Lock Generator > (Albertbox the text appears when right-clicking a visitor) > Suggested text for alert box:
To discourage theft, use watermarks, lower quality images and/or digital watermarking like
Anything you publish on the web can be downloaded and saved. If you have fears about copyright infringement...
1) If you don't have rights, don't publish it.
2) If you own it, Watermark it with your URL or Logo.
3) Digitally register content.
4) Post disclaimers.
5) Cross fingers & hope for the best....
Good luck, Nancy O.
Thereover there is a wonderful philosophical discussion: http://webhome.idirect.com/~bowers/copy/copy1.htm.