This is a technique that you can have great use of. It creates a
"newspaperlook", in other words the image will be built up on small black dots on a white background so it looks like it is printed in a newspaper.
If you have tried the popdots tutorial you will probably figure out the concept of this technique. If you haven´t you will learn a great way to use Photoshops Color Halftone filter.

Lets get started ! The image I will use as example in this
tutorial is the one to the right here with our friend Jolk. You can right-click on it and download it or use one of your own pictures.

Choose Image->Mode->Grayscale. If you have to choose
whether you wish to flatten the image or not choose to flatten it.
Lets give it a bit more contrast. Choose Image->Adjust->Brightness/Contrast and drag the contrast slider to the right to somewhere around +20.

Now pick the Color Halftone filter,
Filter->Pixelate->Color/Halftone. There is a problem here, The minimum amount for Max. Radius is pretty high. So set Max. Radius to 4 ( the minimum ).

Well, that makes us done ! If you want smaller dots however do
like this: Make the image larger, say 200% and apply the Color Halftone filter with the same settings and the then shrink the image back to it´s original size. You may think that that result will look better.