If you only connect some cameras(not all cameras) to your recorder and see the same image showing on 2 or more channels like below, please disable the unused channels to have a try.
Here is how to disable the unused channels:
1 Right-click on the monitor screen, go to Main Menu, click on System.
2 On the system page, please go to Digital.
3 On the Digital Channel page, choose the unused channel number and uncheck the Enable box.