How to embed images into the content of a knowledge fragment?

There are two ways to embed images. One is to write image URLs in content, which must start with "http" (file: is not allowed by the browsers because of a security reason). The other is to register image files as file fragments (there's the text/file switch in the fragment editor) and embed them with the wiki formatting:
 fragment:<another-fragment-number>:embed
Please refer to the Wiki Markup Help which can be opened via the help button [?] in the editor menu.

Fragment Embedding

The text fragment formatting allows you to embed other fragments in the content of a text fragment.
A fragment embedded in another: