Open your image. Press control+u to desaturate it.
Go to filter>custom>High Pass and set the radius around 3.4 pixels. Change the radius according to your image size.
Image after applying High Pass filter :
Now make a duplicate of your layer by pressing control+j. Change its layer style to Color Dodge.
Now go to image>adjustment>brightness/Contrast and increase the contrast of the image so that line edges will be more darker.
As you can see in previous image, there are scratches remained in the face, specially in forehead. We will remove that and all other scratches from the picture by using Smart Blur Filter. To use smart blur filter, go to filter>blur>Smart Blur and experiment with the amount. I assure you that smart blur filter will work very smart :)
Wow, you now have an image which looks like sketch. This is my gift to former Miss World "Ashwarya Rai and Abhishek". Happy marriage ;)
More Tutorials: 
