From Miss Mackenzie:
As we reported last month Jon Bruno has been hired to work exclusively on the CGI ageing process of Renesmee. We have now recently found out and now confirmed by IMDb that Adam Howard, well known for the amazing CGI effects in ‘The Social Network’, has now joined Bruno to assist with the superimposition of Mackenzie’s face onto the bodies on the younger Renesmee’s.
In The Social Network the Winklevoss Twins were made using special effect’s just like the ones that will be used on Renesmee in Breaking Dawn. They were created by having model/actor Josh Pence play one of the brothers in scenes where both Tyler and Cameron Winklevoss are together.
Read more at Miss Mackenzie