I start out by tracing over a section of the image in various media.
The Sassoon bob for the sixties.
Audrey Hepburn for the 40s.
Below is another option for the 50s but it just doesn't communicate the idea of the 40s as well as Audrey Hepburn.
There are numerous photographs that I have attempted this with and the ones that work beast were taken onto the digital editing stage.
Earlier in the development stage of the other designs I was unhappy with the way that they blended from photograph to drawing. So, I had the idea to create a texture to blend from one to the other by tracing the images and transferring them to water colour paper and creating a water colour wash to represent the line from digital to physical.
I will scan this in and try using photoshop tools to create a seem between the drawing and photograph.