holland_derrick,

On the one hand it's dead easy! You simply put the face on a lower (high number) track on the timelines and adjust its size and position to match what it covers.

The hard part is that your head has to be on its own against a plain color background which is made transparent by applying a 'chroma key' video effect to it. The background is typically green as people don't have green skins. How to make a floating head? One option is to Film it against green with a drape to cover the body. If you have an existing image you could paint out the unwanted parts in a photo editing program or use a 'cutout' option if available.

Another method is to use an 'alpha mask' on a track between the regular image and one with the face you want to use. The mask can be a simple head sized black oval on a white ground. When the alpha effect is applied the new face is visible in the oval area and the background bodies show through where the mask is white. This might be easier if your oval is soft grey edged and defines only the skin area and not the hairline.

I suggest trying the techniques with a still image. Getting everything coordinated in a video clip won't be easy!

Regards,

Carl