Lines scrolling through your camera images are a sign of signal degradation and are typically caused by one of two things.

1. The most common cause of lines scrolling through your camera image is signal degradation due to signal strength. If your video cable between the camera and the DVR is too long, or does not have a power adapter of the appropriate amperage, then it is not uncommon to see lines scrolling through the camera.
   
   This can be solved by increasing the thickness of the cable used, using a stronger power adapter, or using a shorter cable. 
   
   
   
2. The less common cause(but it does still occur) of signal degradation is interference. If you know your cameras are powered appropriately for the length of cable they are running through then a source of interference is the issue. Sources of intereference can be caused by the wire running past a high voltage line in your wall, along a flourescent light fixture in the ceiling, or something similar.  Anything that runs a lot of electricity through copper wire creates magnetic interference that, if in close proximity to the cameras signal cable, may cause interference in the image. 

All pre-packaged kits sold by Zmodo already come with a power adapter that is appropriate for the lengths of cable provided with the kit. Should you wish to use longer cables than the kit provides, you will also need to purchase a stronger power adapter as well.