How to prevent wp from generating different image sizes, except for featured img

Hello,
i have a running image sharing website http://cgfrog.com, usually we insert more then 20 images in a single post. I want to prevent WordPress from generating different image sizes for inserted images, except for the post featured image.

For example If there’s 20 images in my post. I want WP to generate image sizes for the Featured image only, and for other inserted images i don’t want different sizes.
Actually the problem is the limited storage space and the other problem is that with those useless image sizes the backup file has more size.

How can I achieve this ?
I appreciate your help.