Hello, Is it possible to add watermark to my pictures which are been watched through Google and no watermark if people are watching my picture through my website? If they click on the pictures on Google, then they will see my website and this picture without this watermark. Picture to understand correctly what I need.
It is possible, if your using Wordpress check : http://wordpress.org/plugins/byrev-wp-picshield-hotlink-defence/ If not it can be hand coded though it's a bit beyond my skills, the information is out there if you need it.
Almost there - just use .htaccess to convert the image request depending on the user agent. Same URL different image. There used to be a really good blog post on komar.org but I couldn't find it. What had happened was he was posting reviews of BBQ's (Grills to those stateside) and people selling on eBay were hotlinking his images and, back then, bandwidth became an issue. His solution was to swap out images requested from other sites with images of tiny BBQs. Your motive is different, and you'll be looking at user agent, not referrer but the rest is the same.