Currently there is no automated means of doing this.
If you manually take a screenshot of a graph you can use the Markdown widget  in a dashboard to render this image and provide a link  to a saved Graph workspace. Example markdown below:
![alt text](https://pbs.twimg.com/media/C22fzEXXgAAv8pi.jpg:thumb "Example graph title")
[Open in Graph](https://localhost:5601/jgx/app/graph#/workspace/bbf6eda0-dccc-11e6-9c56-9bdc3655a367)
Here's an example of a dashboard with the above Markdown widget embedded:
Hope this helps.