Why does Alucard have so many eyes?
Alucard has so called release states those make him less weak. In the manga (Chapter 9 Page 23), when he uses them the first time, you can clearly see that a lot of eyes open on his whole body. The eyes that you see on the picture are most likely the same ones. The reason why he has them is unknown.

It could be that all those eyes belonged to other humans that he consumed during his lifetime. However, this is just an assumption.