The product allows setting a thumbnail for a thread using one of the attachments attached to the thread.
It is possible to choose which image attached should be the thumbnail when creating a new thread or editing the first post of a thread:
The product also adds an icon to current thumbnail/default thread icon allowing to quickly change the thumbnail of threads from thread list (in forum view, What's New page etc.). It also allows to attach an image or delete existing attachments immediately, without having to edit the thread itself: