1 ) open image
2 ) Ctrl + C copy image to clipboard
3 ) menu "Image" -> "Color" -> "Mosaic"
this step we can also apply "Color Tone" , "Splash" , "Black White" , "Pencil Sketch" , "Emboss" etc.
4 ) Ctrl + V paste image from clipboard
5 ) select eraser tool , click and drag on image
6 ) merge all layers

Example :


Local Glass :