Let me start by saying there is no foolproof way to prevent people from downloading images off your website. However, there are a number of strategies that will deter the average visitor to your website.
2. Watermark your images. A watermark directly embedded into your images will make it harder for someone to use the images unless they have really good image-editing skills. However, watermarks can be cropped out unless they’re fairly large.
3. Transparent gif. A transparent gif the same size as your image with, for example, the word “Sample” can be placed over the image. If someone right-clicks to download the image they will end up downloading the gif file, rather than the image itself. Screen shots and editing are still problems, but this method may be easier than embedding a watermark.
4. Post low-resolution images. Low resolution images (72 dpi) are unlikely to be used for hi-resolution printing.
5. Have a copyright statement on your website. This lets people know that the content of the website is officially yours.
Sample copyright statement: “Contents of this web site and all original works are © copyright your name here – All rights reserved. The material on this site may not be reproduced, distributed, transmitted or otherwise used, except with the prior written permission of owner.”
If you find that someone has used your images on another website, DMCA (Digital Millenium Copyright Act) rules require the website host to remove the images if, after notification and any counter-claims, it is found that the site has violated copyright. DMCA official website: www.loc.gov/copyright