images getting resized and blurred

This is a strange problem I have never faced before :

All the images are getting resized to post width and are getting unbearably blurry. They are looking extremely ugly.

example : https://knolzone.com/what-is-cydia-jailbreaking-iphone/ or https://knolzone.com/create-adhoc-network-windows-8/

but, surprisingly, nothing happened to the images in this article : https://knolzone.com/most-amazing-international-border-photos-you-havent-seen/

you can see the images going so horribly bad. I have set the “medium” and “large” settings to Zero but yet I am unable to any change.

I am just unable to add any kind of image smaller than the width of the post.

Can anyone help me solve this problem?