They are called "fan lyric video's." it's a way for fans to take messages or pictures and insert them into an artist's song to make a cool video.
In fact, the video for Tim McGraw, Keith Urban, and Taylor Swift, was a fan lyric video.
This one, for "Southern Comfort Zone" was posted by some die-hard fans and, well, it's pretty cool.
So cool that it got the attention of Brad himself, who Tweeted that he "especially liked the part with Carie Underwood and her 'kids'".
He also added:

Now why did I run like a Cowboy-Forest Gump around Europe for a proper video when you fans go and beat it!