When you make it to the friend that you would like to leave a comment for click on add photo button like I have circled below...
 

 

Than this should show up and you should stay on "Image Info" to add your URL image...

 

Than you pick the Image you would like to add on your friends page from Google, Bing or any other site you use at retrieve you images.  You copy the URL like I have circled below...

 

Than you paste is as I have done and underlined below...

 

Than you press OK to add the image to your comment...

 

It should look like this when you are done adding the URL...

 

After you are done you may add more images/Add a message to you image(s). Than you click on Post Comment on the lower left side and when you post it is may look something like this...

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