Bill Erickson

When you upload an image, WordPress will automatically scale/crop it to many different sizes. If you’re not happy with the auto-crops, use this plugin to upload an alternative image.
If you have images showing up in your theme already, there’s nothing you need to do after activating this plugin. All WordPress functions that provide the thumbnail should now automatically work with your override image.
This plugin will add a metabox to every post type and allow you to modify every image size (built-in and custom ones added using add_image_size). You can use two filters to change these (image_override_post_types and image_override_sizes). For examples, see the documentation.
<a href="https://github.com/billerickson/Image-Override/wiki" rel="nofollow ugc">Documentation</a>
No support will be provided by the developer

Image Override

Allows you to override WordPress' auto generated thumbnails.

shahpranaf

There are instances when one wants to show featured image on single post and hide it on another post. 
This plugin will allow you to show or hide featured image from single post page. It supports custom post types also.
For any query or details please visit <a href="http://shahpranav.com/2015/05/hide-featured-image-on-single-post/" rel="nofollow ugc">Plugin Home</a>

Hide Featured Image

To Hide Featured Image on single post/page.

Image Override vs Hide Featured Image