How to Resize a Whole Face Cut Out in Photoshop
Photoshop may be your tool of choice for serious digital image editing, but it's quite capable of less serious pursuits, such as editing a photo of your friend so his head is several times larger than it actually is. It's not a hard thing to do, but it will take some work, especially if you want the result to appear somewhat natural.
1 Creating the Cutout
Click and hold the "Magic Wand" tool in the Tools bar and select the "Quick Selection Tool." Paint with the tool over the head to roughly select it. Select every part of the head that's above the shoulders, including any hair. If your selection ends up including some of the background and the neck, that's fine, as you'll be refining it after enlarging the head. Once everything you need is selected, press "Ctrl-C" to copy the selection to your computer's clipboard and then press "Ctrl-V" to paste it back in as a new layer.
2 Enlarging the Head
After pasting the head selection into a new layer, press "Ctrl-T" to enter free transform mode. A bounding box will appear around the head. Hold "Shift" and drag any of the four corners of the bounding box outward to enlarge the head while maintaining the correct proportions. When the head is large enough for your liking, press "Enter" to confirm. Press "F7" to open the Layers panel, if it isn't already visible. Select the layer that contains the head, lower its opacity value to 50 percent so you can see the original image through it, drag the head with the Move tool so it's correctly positioned on the neck, and then change its opacity back to 100 percent.
3 Erasing Unneeded Parts
Select the layer that contains the head and click the "Add Layer Mask" button on the Layers panel. This adds a mask to the layer that determines which parts are visible; white means fully visible and black fully transparent, with shades of gray allowing for partial transparency. Press "B" to select the Brush tool and ensure your foreground and background colors are set, respectively, to black and white. Click the layer mask in the Layers panel to ensure it's active and then paint directly on the image to hide anything you don't need, such as the neck or bits of the background. If you make a mistake or change your mind, press "X" to switch foreground and background colors and then paint on the image with white to reveal what you hid. If necessary, press "[" to decrease the size of the brush or "]" to increase it.
Nothing in photo retouching is an exact science, and enlarging somebody's head is no exception. How seamless the finished image will look largely depends on the image you started with. If the person in the photo has long hair that reaches to or past the shoulders, for example, you'll have more issues merging the enlarged head with the original body than if the hair doesn't overlap the body at all. Similarly, a photo taken over a busy background will also make your life harder.