No face detected in saved image

So sorry if this has been answered before.
I run the face detector and save the detected faces as separate images fine.
When I run those saved face images through the face recognition code, it always fails.
No face detected in image.
Any ideas?

Start by reproducing the reported flow in opencv4nodejs: detect a face, save it as a separate image, then pass that image to the face-recognition code. Compare the detector and recognition inputs and document or fix the cause of the "No face detected in image" failure; the issue provides no file or test names.

Written by the indexing model from the issue text.