Start with your base Image

Duplicate the Layer, and select the new layer (Ctrl-L)

Now, go Image>Filters>Blur>Pixelize...

A Box will pop up with the options below, I used 3x3, but it's up to you to find what looks best. Too many pixels will cause you not to see the picture.

Now, you can play with the opacity of it, with dodge and overlay and other layers to get the look you want! I left mine normal so you can see the effect