Lifewire / Miguel Co
The first problem with using a dashcam has to do with obstructing your view through the front windshield, and the second is related to electronic surveillance. Since these issues are dealt with differently from one state to another, verify the law in your location before you start driving with the cameras rolling.
The first legal issue you might run into with a dashboard camera is that most of these devices don't attach to your dashboard. Instead, they are designed to attach to the windshield with a suction cup mounting system.