Capturing the likeness of a person through the artistic representation of facial features is one method of creating a portrait artwork. But there's also variety of other ways in which you can arrive to a successful portrait creation. Here's a few paths:
Here's where you could incorporate analog cut and paste methods or going full digital collage and taking screenshots and then tracing them digitally in apps like ProCreate, Adobe Draw, Adobe Sketch, and others.
AND the combination of various media. Starting with a sketch, taking a photo of it with your phone or iPad, then adding onto it digitally is just one idea... you take the lead and make a creative decision that experiments with these methods! Have fun with it and try something bold!