How do you make a person in a picture appear taller and bigger with photoshop?

Answer 1

Resize the image +200%.

Just kidding! I'd say the trick is perspective. Either paste some images of things that are normally bigger than a person (city bus, tree, etc.) and use the Free Transform tool to grab the edges and shrink it down a little.

Another option would be to use the lasso (I think that's what it's called--not magic wand but the other thing) tool to draw an outline around the person. Then Edit/Cut, paste the guy in a new image, enlarge the image, select all, copy and paste as a new layer on the background you originally cut him from.