At that shutter speed, an airplane moving 600mph would move about less than an inch. A meteor could move a few hundred feet.
Did you only see it in the images later, or did you see it live? It could be a contrail behind a plane, if it persisted for a little while. But if was a brief flash, then I'd say a meteor, or maybe an Iridium flare (moving at 17,000mph).
You could check heavens-above.com for your location/time and see if a flare was occurring. They last for several seconds and can be as bright as -8 magnitude.
The fact that there was more than one makes me doubt aircraft or Iridium, so I'll go with meteor (which was a meteoroid and may or may not have become a meteorite)