Modeling with less reference images? Any good tips?

ISUther

Hello, 

If you have to model a face. 
And you have only one image what you have to model. 
How do you approach this?
I have a image from what i want to model a character face, 
I have similar but not same side view image. 
How would you recommend modeling in this case?
Try to find similar expression face side view?

Burpee

I'm not a an anatomy expert, but it's kinda all about proportion, mesurement and angle, 
You need to have the same triangle shape between the eyes and the mouth in your model etc... Likeness is a real pain to be honest, gl !