How to Prevent copying of the original image folder when the entire website is being copied. Also,what are the measures that should be taken to prevent guessing of the original images.
Just put the original (i.e. non watermarked) images in a non-public folder, inaccessible from the web. When someone want to buy an image, send him using another way, like a CD-ROM.
The alternative is to serve the original images using a dynamic web app, which verifies that the logged-in user has the right to download the image, fetches the image from a protected folder, and then streams it to the HTTP response.
You can't prevent it completely. Custom-build web crawlers can always analyze your site and get the image urls, just like any legit browsers. The best you can do is to detect large amount of access from the same IP, and block that ip when it reaches certain number of hits per minutes.
You can also probably prevent hot-linking by checking the http referrer. This however can be faked by crawlers too.