"I can't hardly see anything." is wrong, dude. It is not unusual though for certain people to talk in double negatives. It is however incorrect English, and you won't here it in intellectual circles.

Where I am from is little more backwoods. We would just as likely say either one. It isn't a double negative exactly. Another example is when people say "I could care less" which is incorrect but still common. They should say "I couldn't care less".