NOT with Photoshop, but rather by doodling onto transparency sheets..
“Storyboard artist and self-described “scribbler” Marty Cooper has come
up with a fun and clever way to augment and play with his surroundings.
By drawing cartoon characters on transparent sheets of plastic paper, he
can place them into real-life situations around him and make his
characters come to life.Dogs, birds, monsters, eggs and vampiric oranges
are all brought through life using plain old sharpies and white-out.”