Lucy Tomas

Very simple plugin that will search for all the first images of your published posts, pages or custom post types and set them as the featured image.
<ul>
<li>You can choose the post type you want to run the plugin on.</li>
<li>Option to overwrite the already selected futured images.</li>
<li>Option to select From / To date.</li>
</ul>

Set All First Images As Featured

still works

It simply didn't recognize any images in any of the posts, and so didn't work. :(

Didn't see the images in the posts

IT works on 5.0.3

Sets the first image of your posts, pages or custom post types as the featured image.

goresponsive

This widget shows you latest posts featured images in a tiled fashion. It is responsive. You can select the category name you want to display images from. Try it out, it is cool.
Demo: http://onion.goresponsive.in/
documentation
http://goresponsive.in/news-in-pictures-widget/

Go News In Pictures

Plugin for viewing best news photos, news pictures online

Set All First Images As Featured vs Go News In Pictures