Go to the Commons tool.
Select the Commons tool from the Tool Menu of your site.
The Commons page will display.
The text box at the top of the page will always start off with "What's on your mind?" until you type something into the box.
Click the Insert a link button.
Click the Insert an image button.
Select the file.
Click on the name of the image. Then click Open.
Click Post to submit the post to everyone on the site with access to view it.