QnAMaker makes use of markdowns to store answer text. The rendering links will depend on what formats are supported for the channel. Different channels support different rendering formats and a specific format might work in a particular channel and might not in another.
Example:

Similarly, for rendering images, you can add images to a QnAMaker answer by adding the URl via markdowns.

The knowledge base supports Markdown. However, the auto-extraction from URLs has limited HTML-to-Markdown conversion capability. If you want to use full-fledged Markdown, you can modify your content directly in the table, or upload a knowledge base with the rich content. Multimedia, such as images and videos, is not supported at this time.
Also, QnA Maker doesn't process the image in any way. It is the client application's role to render the image.