Nasa:

In December of 1968, the crew of Apollo 8 became the first people to leave our home planet and travel to another body in space. But as crew members Frank Borman, James Lovell, and William Anders all later recalled, the most important thing they discovered was Earth.

It can be argued the picture, “Earthrise”, was the one photo that changed the earth the most. It expanded our understanding and concern for the planet we live on.