Here, I have an image of actress Troian Bellisario. I have taken this image from IMDB.com.

(Ron Brown, unknown date. IMDB.com. Troian Bellisario.

I have created a new layer here.

Here, I have lowered the opacity of the image to make it easier to draw around. I have also selected the paint brush tool.

Here, I began drawing the outline.

I then continued to draw the silhouette until I was happy with it.

I then completely lowered the opacity of the image which then gave me my finished image.