Photo realistic artwork can be created by tricking the eye with implied depth, using photo reference and digital painting software, or by spending a really long time making sure every detail is perfect on each piece.
Italian artist Emanuele Dascanio has chosen to go with the latter, and he spends hundreds of hours creating each one of his incredibly realistic portraits.
Emanuele uses the chiaroscuro related technique of single source lighting to help sell the realism, and he works primarily in charcoal, graphite and oil paint which make it easier to create high contrast imagery on white canvas.
Here's a video showing his full creation process from start to finish:
-Via Time Wheel