How can i add og tags for example in to articles ?

<meta property="og:image" content="http://linkmotor.de/images/linkmotor.jpg">

When i switch to source code, for example in articles. Then i add this but after save the code is deleted automatically.

Why and what can i do about it? I want Facebook and other social media sites to properly pull the right data parts.

"og:image" is added automatically in modules with images, since Articles module has no image upload functionality then this tag isn't added. 

It maybe there is some 3rd-party module which adds such functionality.

Ok, i understand why it is not added automatically.

But why is it DELETED automatically when i added the information manually ?? Why does the editor strip my manually added code?

if article is added as admin it shouldn't strip anything on server side, however TinyMCE may strip some code.

You may want to check out the Advanced Articles module that allows you to add Photos. The "og:image" tag will then be automatically added.