Start with a JPG or GIF file. If you use a GIF, increase the color depthto 16 Million colors (Colors, Increase Color Depth: 16 Million Colors.)The best photos to use are ones that are fairly light and have a lot ofcontrast between objects and their backgrounds. If your photo is too dark,try increasing the lightness (Colors, Adjust: Hue/Saturation/Lightness).Here I've chosen a pic that I downloaded from ArtToday.
 
 
 

First, we add a little Noise. Go to Image, Noise:Add. Check UniformNoise and set the slider to 15. Your photo will get just a bit grainy.
 
 
 

After adding the noise, we sharpen the photo. For this image, I appliedthe Sharpen More filter twice (Image, Sharpen: Sharpen More). Dependingon your photo, you may need to Sharpen or Sharpen More an additional time.You should notice that the grainyness has increased considerably.
 
 
 
 

To complete the process, all we do is decrease the color depth to 2colors (Colors, Decrease Color Depth: 2 Colors.) Check Grey Values as thepallette component, Weighted for the pallette weight, and Nearest Colorfor the reduction method. There you go...a pointilized image.
 
 
 
 

A quick word of advice, it may be necessary to clean up your image abit to get this tutorial to work. For example, if the sky in the photoabove had been too dark, I might have needed to select it with the lasootool or Magic wand and lighten it to give the necessary contrast. Don'tworry if there are jagged areas when you're done. The conversion to dotscan hide a lot of tweaking.