For videos and photos, they use 'exemplary' people in Bethel and congregations in the area. They actually have files on these Witnesses and they note if one of them is no longer exemplary. If that happens they will replace them in photographs whenever they update the publications. The most notorious publications for this are the Young People Ask books (for obvious reasons).
I'm guessing it's too expensive to do this for videos but I'm sure it would happen if feasible.