How to Force WordPress Posts to Have Featured Images
Many WordPress themes rely on Featured Images, but they can be a mystery to many users.
What exactly is a Featured Image in WordPress?
A Featured Image represents the mood, or theme of your Post.
Posts and pages normally have a single featured image.
If you're new to WordPress, you'll find the “Featured Image” box on the right-hand side of the screen when creating posts. If you don't see this option, check your Featured Image permissions.

Click on the “Set Featured Image” link and this will open the WordPress Media Uploader. You can use that to upload an image from your computer or use an existing image from your Media Library.
How Are Featured Images Used?
How Featured Images display on your site is 100% decided by your theme.
Take a look at the blog post below. On the main blog page, the Featured Image is on the left-hand side.

However, if you click through to a single blog page, the Featured Image has moved above the main text:

Almost all themes support Featured Images, but if your theme does not, here's how to add Featured Image support to a WordPress theme.
Why Force Writers to Include Featured Images?
Here's a key thing to know about Featured Images … many themes will look strange without them. Many designers create themes that look great with a Featured Image but look slightly odd and sparse without them.
So if you want to force your writers to include Featured Images, how can you do it?
The answer is the PublishPress Checklists plugin.
- Install PublishPress Checklists.
- Go to Checklists > Settings.
- You can choose “Featured Image” as one of the items that authors must complete before publishing.

What do these options mean?
- Show a sidebar message (default): This simply shows the recommendation in the sidebar when writing a WordPress post.
- Show a pop-up message: This will display a pop-up with a warning message, but users can still publish.
- Prevent publishing: Users won’t be able to publish if this is not complete.
Now when someone goes to write a post, this is what they'll see in the sidebar:

After you've uploaded a Featured Image, the red X will turn into green check mark:

For for details, check out our guide to forcing users to add featured images and controlling the size of featured images.
Summary
Featured Images look great on your site and help visitors get a quick feel for your content.
However, Featured Images are not required by default. If you want to create a site with consistent, good-looking, high-quality content, then make sure you have a stylish Featured Image for each post. Use the PublishPress Checklists plugin.
Beyond just Featured Images, PublishPress Checklists also allows you to force a minimum and maximum number of words, or even add your own add your own custom rules.
Force WordPress Posts to Have Featured Images has
minimum width and minimum height
maximum width and maximum hight,
also If you can make Require a Minimum Image Dimension for Uploading!
https://wordpress.stackexchange.com/questions/28359/how-to-require-a-minimum-image-dimension-for-uploading
why you don’t add the minimum and maximum number for internal Images.
Hi Audai
Thanks for the idea. I don’t think we can control the Media Library uploads, but we could add a max and min option for the height and width.