[Co-Authors Plus](https://wordpress.org/plugins/co-authors-plus/) is one of the most useful plugin for multiple authors blogs. This plugin add a widget to add users' avatars to post also for guest authors and for posts with multiple authors.
You can also add avatars with a shordcode [blog-post-coauthors].
1. Make sure that Co-Authors Plus is installed and active.
2. Extract the widget-for-coauthors.zip file and upload its contents to the /wp-content/plugins/ directory. Alternately, you can install directly from the Plugin directory within your WordPress Install.
3. Activate the plugin through the "Plugins" menu in WordPress.
4. Add the widget to your sidebar or the shortcode to your posts or pages.