This is a really simple thing to do, but it has a lot of steps. When you memorize the steps it can take as little as two or three minutes. Ready to try it? Let's go!
First of all, you want to open the image you'll be using.
The next step is to add a new layer on top of our image. We do this because we can't whiten and do all the other effects we need to directly onto the image. Everything on the new layer (like laying a transparency over the image) will show up on the image, but will not be permanent. Until we save it, that is. :0)
In my next few images you'll notice my 'Layers' box is missing. Just ignore that, ok?
Now we want to zoom in until we can see the outline of each individual tooth clearly.
Now select the paintbrush tool from the skinny box on the left side of the screen. Set the brush width to three. Then go to your color palette and click on white. Now draw an outline around each tooth, making sure you connect the start and end of your lines. This is important for our next step.
Now select the paint bucket from the tools box. Make sure white is still selected on your palette, and fill in each tooth. Just click once inside the outline of each tooth.
Looks like a mouth full of Chiclets, right? We're going to fix it, don't worry. Go to 'Effects' at the top of the page, and click 'Blurs'. Now select Gaussian Blur.
Set the radius to two or so. You don't want them so blurry you can't tell the outline of the teeth. Mess around with it until you think it looks good.
See how it's made a softer outline? This is good; exactly what we want. Now, it's still weird-looking, so we need to make a few more adjustments.
We're going to click now on 'Layers' at the top of the screen. Then slide down and click on 'Layer Properties'.
In the box that shows up, set the opacity to about 62. You can change this depending on what look you want. (Not sure where my pic went, but I can't find it. Sorry!)
Now we'll choose 'Layers' again, then 'layer properties'. Now we'll click on mode: overlay. Set it to about 81. Fiddle with this one too, depending on the look you want.
You can go back in now and do the same for the bottom teeth if necessary. Start by adding a new layer, and follow all the directions the same way.
In the box that appears, click on the 'Save as Type' box, and scroll down to choose either GIF or PNG. Both are widely used formats. If you work with Paint.NET doing other things, you'll quickly learn that Jpeg format does not save nicely.
When the next box appears, click 'ok'. These default settings are fine for what you're doing.