It is extremely difficult to make a believable look alike.
You need all the pictures you can get your hands on, and in the highest resolution possible, as reference material.

General shape is easy.
But eyes, nose and mouth HAVE to be exact and can take weeks to get right, to make a believable look alike.

Good luck with your project.

Poser 1, 2, 3, 4, 5, 7, P8 and PPro2010, P9 and PP2012, P10 and PP2014 Game Dev
"Do not drive faster then your angel can fly"!