According to the FX Guide, Lola VFX initially planned to achieve “Old Peggy” by filming Atwell with no make-up, "do a further shoot with old age prosthetic make-up applied," and then "carry out a digital facial re-projection of the ‘old age make-up Atwell’ onto her original body." However, due to the prostetics “restricting” the British actress’ performance, the Captain America: Winter Soldier crew resumed the make-up process with a young actress that resembles Hayley Atwell.
Then an elderly actress was cast and brought in “with the intention of seeing what real skin looked like; translucency, how does the skin sag, how does it move as she talks?” said Williams. “I said, ‘Let’s try something that we’ve never done before.’ I wanted to take the performance of the elderly woman that we had shot in a rig with eight cameras and project the skin onto the original Hayley footage that had been shot on set. We took a still frame of the skin and tracked it onto the original photography, and it looked so good. The way we did it – it was amazing – you could still see Hayley, her eyes, her mouth, her underlying structure, but we just lifted the creases and cracks and age from the elderly woman and transposed it onto Hayley’s young face.”
For an even more in-depth explaination as to how the Lola visual effects team created “Old Peggy,” make the jump over to the FX Guide. However, you can see a shot of Hayley Atwell’s Winter Soldier scene compared to the finished product, and other official stills via Luma Pictures.