The images on my home page are sometimes replaced with small black boxes
Can you please provide more details about the issue? Maybe along with screenshots.
Here is a screenshot of what I'm talking about. I hope this helps us come closer to a possible solution. Thank you for your assistance!
Black box means? Are you talking about broken profile pictures? If yes, it's not related to rtMedia plugin. Those profile pictures coming from BuddyPress and WordPress gravtar.