Use separate portraits when possible
One person per photo gives each role a clean identity reference. Keep the face large enough to inspect, both eyes visible, and hair unobstructed. Similar lighting across the two inputs can reduce abrupt identity changes.
Avoid ambiguous group shots
A group photo makes role assignment less reliable. If you only have a photo of both people, crop two separate copies around each face before upload. Do not use a screenshot with interface text or a heavily compressed social-media thumbnail.
Review the transition carefully
Identity drift often appears during fast motion or the hard cut. Check the run, the embrace, and the healthy memory version of both faces. A higher resolution adds detail but does not automatically fix a weak reference image.