You should be able to use the valid_elements property in a TinyMCEPluginNonVisual. There you can make sure that the TinyMCE-instance removes height and width by itself.

It's probably wise to strip them out using Save events on the server side as well. Then you won't get any surprises if for example someone starts saving HTML from some source programatically.

Not exactly what I want :-)

I want to be able to use width and hight (manually), but the button itself should not inject the attributes.

How can I alter the behaviour of the button?

OK, after 7.6 it's hard to "hack" the original plugin so best way is to copy it  as your own plugin, maybe an option could be to work some URL rewrites and catch the script in question and just make a little modification.

The documentation have some info: http://world.episerver.com/documentation/Items/Developers-Guide/EPiServer-CMS/9/Editing/Customizing-the-TinyMCE-Editor/

Fredrik, did you solve this? to no fill in automatically the fields... 

My customer gets totaly wrong propotions too...