There are many softwares that can do this work. Photoshop is one of those but it's a bit too complicated to use it. I prefer to use an easier one called IPhoto+ V 4 - the tecnic is quite simple: first of all I highlight the veins already visible in the picture. To do so, it needs to make them slight clear using the good size brush and following them. The second step is to add shadows on just one side of the veins using the brush darker. In this way the veins become more visible. Of course it needs time to practice but sometimes the result is very good.
