I know water mark the photograph is one method to protect ones copyright over the picture. is there any other technique through which one can prevent or detect the plagiarism of photos.
There's not any fool proof way. If you upload or host a photograph on a server and it's accessible by users or it's accessible by anyone with an internet connection the content becomes fair game for anyone to take/reuse/re-upload/edit/copy.
Here are some mechanisms that certainly slowdown people form misusing your content:
Watermarking (as you mentioned)
Stenography can be used to hide information in the photo that lets you do an image search via google's image search and always find instances of your photo, then you can ask the user to remove the misused content.
Preventing users from taking screenshots (poor form and i.e only)
Preventing users from right-clicking image