Start with a photo that you want to turn into a two tone silhouette.
Duplicate that layer by pressing Ctrl + J, than desaturate it by pressing Ctrl + Shift + U.
Go to Filter -> Artistic -> Cutout and apply these settings.
After applying the effect the photo should like like this
Press Ctrl + L to bring up levels, drag the sliders together until the photo is just black and white.
Now go to Filter -> Blur -> Gaussian Blur and set it to 1.0 pixels to get rid of the jagged edges.
To smooth the edges a little just bring up the Curve dialog by pressing Ctrl + M and adjust it till the edges are crisp.
Your final product should like like this.
