"How can I prevent my site visitors from stealing my images?"
There are various methods for trying to prevent your site visitors from saving copies of your images to their own PC's. None of them works, so there's no point wasting your time with them. Here's why:
With many skins, the address of the image can be determined very easily, so the visitor can go directly to it, at which point you have no control over what he does with it. If the slide page address is http://example.com/slides/mydog.html, it doesn't take a genius to figure out that the image address is probably http://example.com/slides/mydog.jpg. With some skins, the browser's status bar will reveal the URL of the image when the visitor mouse-hovers over the thumbnail.
Even if a skin doesn't immediately reveal the URL of each image, a user can always view the source code for your pages and quickly determine where the full-sized images are. This is true even of Flash skins - by opening the relevant XML file in a text editor, the image names and their addresses can be discovered.
Once a visitor has determined the URL of the full-size image, hotlink protection on your server might thwart this approach, but it might also make it impossible to render your pages (particularly if your album contains videos).
Before an image can be displayed in a browser, it is first downloaded to the visitor's PC, and stored in his temporary internet storage. The visitor is not viewing the images on the server, as if through a telescope. The images are already on his PC when he first sees them. Therefore, a user can retrieve those images from the temporary storage on his PC.
Finally, a visitor can grab a screenshot and save a fairly good version of the image he's viewing.
The bottom line is that you can't protect images that you put on the web. You can watermark them, which makes them ugly, or use low-res images that no one would want to steal, which makes them ugly. A knowledgeable user will always be able to grab the image.