Modifying post image output.

I’m trying to figure out how to overwrite the function that outputs images that are used in posts. Essentially all I’m looking to do is wrap that output in div tags. I did it for the img_caption_shortcode function that outputs images for pages, but for some reason posts don’t use the same function. As a matter of fact, the html for the post gets stored in the database, including the img src, etc, so whatever needs to be modified would appear to be an admin file/function.

Any help would be appreciated.