The process of carving from a photo starts from the photo itself. Since I'm not that proficient in digital imaging, I use a lot of apps (Phot0shop, Picasa, Phot0Scape, MSPaint, etc) to get a clear image. For normal clear (to our eyes) photo, I still need to clear the effects of shadows and lightings before turning it into a sketch. Then, render the sketch to the best image fit as possible. So, imagine if I get a blurry photo or a small photo... I would need to blow it up and fill in the pixel to the best that I can.

Now, even if you get the sketch to look like 100% of the potrait's features, there is the process of transferring the image onto the eraser.

One method is tracing all the lines on the image with a pencil, put the image face down onto the eraser and proceed to scratch the back of the image with pencil. Even then, you may not get the image 100% correct. You will need to trace the image on the eraser with a pencil and be careful that you wont change the image of a baby to an old woman (that may happen depending on the state of the hand that day).

The other method is to go and buy a bottle of nail polish remover (important ingredient: acetone). This will make your life easier, provided you typed/drew the text/image correctly. Put the image face down on the eraser, use a clean white kitchen towel or serviette and apply some of the nail polish remover on it, dab on the face down image till you can see the text/image from the back of the paper.  Lift the paper and voila!!! text/image is transferred! 

Of course the ultimate challenge comes during the carving. At most you can get 60% similarities. When lucky, you get 80%. When a miracle happens, you may get 95%. So, lots of praying is needed ;D

That said, I have yet to start carving the above headshot. I just transferred the image to the eraser this morning.