This is one of over 4598 effects generated by Filter Forge, a Photoshop plugin that allows you to create your own filters.
This effect:
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To open this filter, you must have Filter Forge 3.0 or higher installed on your computer. If you don't have it installed yet, click here to download Filter Forge
The first computer graphics I ever saw was a picture of Snoppy printed with a dot matrix printer where the detail and shading was created by different combinations of letters and numbers. This filter kinda does the same thing using a small version of the image itself to create the texture shading. You can change the size and color of the texture and even add outline for more detail. I couldn't use Snoppy as an example image, but I think you get the idea.
texture, pattern, background, dot matrix, Snoppy