Statigram, the same app I mentioned on a previous post has a cool feature to help you promote your instagram photos as well as to take advantage of your images already posted to instagram.
If you go to statigram, you can visit the promote tab and allow it to create a Facebook cover photo based on your latest instagram photos.
It's a pretty cool little feature that Statigram offers, and just like the app itself, it is free. Every month or so I switch out my cover on Facebook and I use one of the covers created using Statigram.
This is my latest one:
The one thing I did was change the branding from statigram to my own website, the part that says "notagrouch.com" But the rest of it was all done automatically for me and it takes just a few seconds to create.