Open an image for applying the cracks to.
Double click the Lasso Tool on the tool bar to select the Tool and to bring up the Lasso Options. Make sure Anti-Aliased is Unchecked and feather is set to 0. This is so we know it will be nice and sharp and no smoothing or soft edges
Make a New Layer. On the image now, jiggle the mouse and make a crack of some sort with the lasso. You’ll need to start at one point and then eventually return to that same point (like shown). This takes a little artistic skill from you to make a really cool one. So if you don’t like the first try, then hit undo.
After you have made a crack design, fill it with 100% white by using the paint brush or going to Edit>Fill and choosing White.
Offset the selection one pixel up and then to the left one pixel using the arrow keys on the keyboard.
Fill the selection with Dark Gray. Now choose "Hard Light" from the layers pop down menu.
You can Deselect it now by going to Select>Deselect.
To add the hollow look, go to Layer>Effects>Inner Shadow. If you don’t want this look, then fill with Black instead of Dark Gray on step 5.
This next step we will be adding some details to the cracks.
Zoom into an area. Paint some Highlights above the crack and a dark shadow below the crack like I have shown, this makes it looked popped out a little. You will need to be creative and artistic, try and play around a little bit.