Bobby wasn't sure what made him do it, but just on impulse, he took a photo of those two idjits.
They'd just wrapped up a hunt in the mid-west, and the sun was just going down after an oppressively hot midsummer day. The impala was parked on the shoulder of the highway in the middle of nowhere (which most of the mid-west was). It was just a moment, a fleeting moment in time, and Bobby happened to have his crappy old camera in his hand. The film in it was well past its best, and as a result the picture was a little out of focus, but somehow it worked.
After he developed it, Bobby sat and gazed at the picture for what seemed like forever. He knew that what he'd captured, was something intangible and precious; something he couldn't put into words. He knew that this picture showed what lay below all the bickering and fighting and pranking and general piss-taking that happened between the Winchesters.
Underneath the picture, he wrote 'brothers'