Inserting images and preventing the layout from breaking The client has asked for an auto resize of images (when inserting via the ckeditor) so to avoid the breaking of the layout, and including images that are just too big. Is there a way to automate this process? Do you normally offer this? Or do you just make the client aware of the width and height settings in the image properties window?
Image styles are built into Drupal 7. You can define image styles to have a particular size, by either cropping, scaling, or some combination of the two. Drupal 7 also supports scaling only down but not up.

If you want to do this in Drupal 6, you do it by installing the Imagecache module and configuring your styles with that.