The 515 doomed passengers and crew in this shot are both real and
computer-generated—trick question! All of the passengers in this shot, from
first class to steerage, were created digitally, but the motion for the
"synthespians" was provided by live actors via motion capture.
For this technique, the actors wear reflective markers at
key body joints, and surrounding cameras sense reflected infrared light,
recording their body movements in the computer. Later, this motion is applied
to the digital character. Fewer than 20 performers provided the motion for
hundreds of virtual characters in "Titanic."