Images in TinyMCE editor do not auto adjust for smaller sized windows. But they could...
If you add "max-width: 100%; height: auto;" to the <img style> tag on a
picture that is inserted in a Tiny MCE editor it will make the photo image adjust in size proportionate to the size of the window.
Right now if you look at a page with an image inserted in a Content Editor App, from a phone or a tablet, the image does not adjust in size automatically. There is not a true "Responsive Design" element for that image. This can cause the end user to either not see the image correctly or force them to use scroll bars.
The width element of 100% means that it will not get larger than the set image size. The auto height element allows for the image to shrink as needed.
I am proposing that "max-width: 100%; height: auto;" is automatically added to every image that is inserted into a TinyMCE editor app.