This plugin replaces the mjpg-streamer on the control tab with the static snapshot image and updates it with a javascript interval timer. You can set it to only do this if the mjpg-streamer fails.
This plugin could be useful if you're using a browser that doesn't support mjpeg streams (IE) or if you would like to reduce bandwidth usage when accessing from the internet perhaps.
pip install https://github.com/MarkWal/OctoPrint-SnapStream/archive/master.zip
Make sure you use the same Python environment that you installed OctoPrint under otherwise the pip install will fail because the plugin won't be able to find its dependencies. For octopi this means:
source ~/oprint/bin/activate
before you do the pip install.
Restart OctoPrint and the octoprint.log should show the plugin was successfully found and loaded.
This plugin uses the url's for the webcam from OctoPrint's webcam settings panel so the snapshot url has to point to something your browser can reach.
In the settings panel under SnapStream you can choose fps (probably needs to be something low like 1 or 2). You can also select whether to use the snapshot mode all the time or only when the mjpg stream fails.