Step 1:

Open the photograph to be cartoonized with your computer drawing software (you can use gimp or photoshop, or any other good photo editor software).

Step 2:

Isolate the object. Clear out all unwanted parts of the photograph.

Step 3:

Create the outline of the picture.

Step 4:

Add color to each part of the picture.

For this example, our first part to be colorized is the skin...

Step 5:

Now that we've done coloring the picture, let's apply some shading to give depth to the picture.

Step 6:

Last step. Add a background.

That's it!
Now we have the cartoonized version of our photograph.

Next:

Now that you already understand the overview of photo cartooning process, would you like to know the process details? Would you like to know how to do those steps using photoshop?
If you're still interested, let's move on to the detailed tutorial.