Turning an image into a halftone pattern.
To halftone an image you first need to prepare it, if it is a photograph or image with shadows and highlights present you should first, if it isn’t already, turn the image greyscale then increases the shadows and highlights using the Levels adjustment.
Now go to Filter -> Pixelate -> Colour Halftone Stay within 5-15 as that is the recommended range and set all channels to 45 and press ok.
You now have a halftone image, you can now turn this into a brush simply by selecting your image and gong to Edit -> Define Brush Preset, choose a name for you brush and press Ok, and you have a brand new Photoshop bursh you can use. Having an image as a brush makes it very convenient to use and place it in your work.