Author: Matt Gentile
I came across this problem while I was coding one of my Buddypress installs. One of my installs is completely custom PHP code and I had a situation where the featured image would not show up in the activity stream associated with a blog post.
This Literally took me a year to find/mess with and code the official thing. This code will 100% get the featured image in the specific post id to show up in the associated Buddypress Activity Stream Item's excerpt/content.
Place the Following code in your functions.php file and this will work universally:
Just like my freebie posts, you are required to link back to this site any time you use this code.
License Info: Creative Commons Attribution 3.0