Is it possible to create a template to style the image in the editor?

Probably not the best description, anyway what I am hoping to achieve is to style the image for all content. Currently I can’t find if the generated html for adding an image, doesn’t seem to allow this in ContentBox. I would like to apply a drop shadow to my image, but to do this I would like to apply a div right under the image.

So question, is this already possible and secondly where would I begin looking to change this behaviour?

Could you add a style to the current theme’s stylesheet?

Something like img {box-shadow: 10px 10px 5px #888888;}

It isn’t the solution, what I mean is that when you use the filebrowser to add the image to the content, it inserts the code to align and display the image. I am in need to insert the template that I need for my theme.

Does that make better sense?