The video below will show you how to create a custom digital prop.
Specs: This is not exact as it would depend on the shape of the prop but you can work with 1200px by 1200px.
Please see below for the recommended points for each specific type of mask/prop (selected points are displayed in green)
Best for glasses or masks over the eyes
Best for hats or head props (bunny ears etc)
Best for beards
Best for Mustaches
Best for Eyebrows
Best for nose props
Best for props under the face, i.e. a Bowtie etc