The photographer himself recovered the glass plates of those photos by diving into the freezing Antarctic water after the ship had sunk. Shackleton ordered the remaining plates destroyed (the ones still on the sunken ship) so that the photographer would not risk his life a second time to recover them.
The network you saw a movie on Shackleton was A&E. In fact it's on tonight at 8 PM (Eastern). This is not the same movie that we saw.
Actually, they are different. The one last week (I watched it) was a documentary with archived footage. The one this evening and tomorrow is a re-enactment with actors.