Images are not reponsive

Hi,
How can I make the images I add to the website responsive ?
I can see images displayed in some articles (Gallery or Blog) are fully responsive
but when I create a new article and place some images using the editor (JoomlaCK), They are distorted when the screen is reduced.

Any idea ?
Thanks

Hi,
I thought that Senior Boarder knows that images must be without width and height added in their style.
I guess that JoomlaCK adds it automatically,
JCE is much more smarter in this topic.