i satarted by making a duplicte of the background picture i got from http://www.inkedone.com/painting/mixedmedia/woman-portrait-by-patrice-murciano,

next i  added a Solid Color fill layer to serve as the background color for the effect by adding an adjustment Layer icon at the bottom of the duplicate layer, then I added a mosaic filter under pixelate in the filter menu. Finally added a 6x6 px circle i had predefined as a pattern by adding a layer style (pattern overlay) and changed the blend mode to multiply