Charmed

 "This is the last time the audience sees the original ""Three"". Shortly after this moment, their secret is revealed, Piper is shot, and in order to save her sister, Phoebe makes a deal with the Source, which causes time to be reversed. In the new timeline, Shax attacks and kills Prue. Prue's death effectively ends the first era of Charmed.

This ""photo"" becomes haunting because it represents everything they lost. It is an image of a complete family, an unbreakable force of Three. Looking back, their smiles in that scene become painful, because we know that it is their last smile as three.

For Prue, this is her last image as a sister, a witch at the height of her power and fulfilling her destiny. She left as a hero, and this brief moment of happiness was her unofficial farewell to the audience.
Before this episode, no matter how many dangers the sisters faced, they always found their way back to each other. They always won. ""All Hell Breaks Loose"" was the first time they paid such a high price. That ""photo"" symbolized their innocence and the belief that they would always be okay, a belief that was broken forever."