Hi kjell.ek,
Please refer to http://richtexteditor.com/document/scr/html/auto-image-resizing.htm
you can set in config file "\richtexteditor\config\default.config", the section below.
<!--allow,resize,deny-->
<security name="LargeImageMode">resize</security>
Or in code
Editor1.SetSecurity("*", "*", "LargeImageMode", "resize");
Regards,
Ken