How to prevent downloading images and video files from my website?

Put your image or video in flash format. Works great.

I believe THEOplayer already provides this sort of solution as a paid service, but I'm not so sure about it.

DRM solutions are available today. It makes the video viewable but not downloadable.

What is DRM?
Digital Rights Management (DRM) solutions are software programs created to help people protect and control their valuable digital content, whether it's documents, videos, images, or audio files.

Check out this. Hope it's helpful.

If you want only authorised users to get the content, both the client and the server need to use encryption.

For video and audio, a good solution is Azure Media Services, which has content protection and encryption. You embed the Azure media player in your browser and it streams the video from Azure.

For documents and email, you can look at Azure Rights Management, which uses a special client. It doesn't currently work in ordinary web browsers, unfortunately, except for one-off, single-use codes.

I'm not sure exactly how secure all this is, however. As others have pointed out, from a security point of view, once those downloaded bytes are in the "attacker's" RAM, they're as good as gone. No solution is 100% secure in this case (please correct me if I'm wrong). As with most security, the goal is to make it harder, so the 99% don't bother.

I think the best way is to prevent right clicking on your webpage, because that is the most convenient way a normal user try to download the content, and you can consider it as remark if u able to do this only as you are never gonna be able to stop a computer geek or hacker people from downloading it, because once the content is on the internet, it means it is in the public domain already...

Put the content on google drive and make it download protect. This way people can only see your documents, pictures but cannot download it.