My LR Classic catalog is stored on my MBP - but the actual pictures are stored on an external HD - do I need to have the External HD mounted in order to complete the Face Recognition ? or I could do the process on the MBP hard disk using the previews ? Thanks !
Victoria is correct. Normal JPEG based previews won't work in Lr's case because Lr needs to support non-destructive edit image workflow. Those JPEG previews could be cropped, rotated and transformed after applying the develop adjustments. Lr wants to run the face tagging only once on the original unaltered image data.