Whitening Your Teeth
Open the photo that you want to use to whiten teeth. The photo I used is shown below:
Next we will duplicate the photo so we will be able to compare the enhancement to the original. Click File > Duplicate:
We will work on the copy of the teeth. Now we will need to zoom into the photo by clicking the zoom tool and then select the magnification from the zoom options panel:
Now you should have two pictures open. Now we need to select the teeth. Select the Magnetic Lasso Tool:
Begin left clicking around the teeth arrow. This is creating anchor points around the focus area:
As you will notice where the magnetic lasso got its name. It acts as a magnet around the teeth. If the Magnetic Lasso sets an bad anchor point, just hover over it and press Backspace or Delete. If you don't get the results you want, you can select the polygonal lasso tool to see if you get better results. Continue clicking until you get back to your first anchor point. Your selected area should look like the picture below:
Jump the teeth to their own layer (Ctrl + J). With the teeth layer selected (it will appear blue in the Layers Palette):
change its blend mode to Screen, as shown below. Brace yourself as the teeth will become extremely white, looking unnatural. We will fix that in the next step.
To lesson the white effect, lower the opacity of the teeth layer until you get the desired effect.
Here are my before and after shots:
Now click back on the original teeth photo to compare your picture. If you want to save the photo, Click File > Save As> and choose JPG as your file format: