Filter IMG from post, add something and ECHO it back to the content

Hi everybody!

I’ve been breaking my head over something, so i hope somebody can help…

How can i filter every img from a post + featured img, and after filtering it put it right back in the content at the same place BUT with adding a shortcode below the <img> tag..

I’ve found something like this which seems to somehow come close to solving my problem, but i’m not sure: possible solution

So basicly, dynamicly check a post or page for and img (or featured img) and if so, put s shortcode beneath the img tag (in this case shareaholic shortcode).

Thanks a lot for the help!