This will also work on color photos, however, I really like what it does for black and whites. Here you go:
1) use whatever process you prefer to convert your image to B/W (but do so while maintaining the color channels)
2) open up the channels palette (that’s one of the tabs you’ll see on the top of your History palette)
3) hold the control key (on PC’s, Mac may be Alt key??) and click on the RGB selection in the Channels palette. You will see the marching ants show up in your image
4) make a new layer (Ctrl J) and click on Overlay (Softlight will also work with a little less intensity)..WOW!
5) adjust your slider opacity to taste Flatten layer
Please feel free to share your comments and your results