Shane Gowland

This plugin adds support for Topic Thumbnails with bbPress. It works by retrieving the first image from each topic and displaying it alongside the topic title on the index page. Thumbnails are sized according to the default ‘thumbnail’ size in your WordPress media settings. The images will also resize appropriately if you’re using a responsive WordPress theme.
This plugin works with GD bbPress Attachments and most other bbPress image management plugins.
If you enable this plugin while bbPress is disabled (or not installed) it will display a warning message.

bbPress Topic Thumbnails

Provides bbPress with support for topic thumbnails.

Coronoro

Simple Plugin which shows whether a registered user has read a Post or not. 
You can also choose to show the number of unread Posts at Forum level. 
This Plugin is an update to the older <a href="https://wordpress.org/plugins/bbpress-unread-posts/" rel="ugc">bbpress-unread-posts</a> Plugin.

bbPress Unread Posts v2

Simple Plugin which shows whether a registered user has read a Post or not.

bbPress Topic Thumbnails vs bbPress Unread Posts v2