When the recorder or client shows the device online and the stream is running, a completely black picture means the link is healthy and the fault lies in imaging or decoding.

• Protective film left on the lens: the most common oversight on a new install. The factory dust sticker blocks virtually all light.
• Exposure and gain clamped down: a full-colour model at very low light with the illuminator off and a low gain ceiling will render an almost black image. Raise gain temporarily or force the illuminator on to confirm.
• Illuminator not working: a faulty supply to the IR or white-light LEDs, or a misjudged photocell threshold, leaves night scenes black. Point a phone camera at the LED board to see whether the IR emitters glow.
• Stream and decoder issues: switch from the main stream to the sub stream, or try a different player, to rule out a decode failure caused by aggressive encoding settings.
• Obstructed lens: a wall, decorative element, tree branch or cobweb blocking the field of view.

If all of the above check out, pull the device log for sensor initialisation or IR-cut filter switching alarms.