P: Search by photo

Imagine a scenario: I have tonnes of gallery folders in my lightroom account that i have accumulated over many years and I need to look for a photo of a person that i know I had taken a photo of some time back. I have a photo that I see online of that person, if I can download as a sample and use it in my Lighroom photo search to find the same face of the person that I have in my gallery - this would be a great feature, esp. for those of us who get last minute request for a personal photo.