Is there a Linux camera app?

Cheese or GNOME Camera (Snapshot) are common.

Why does the browser show two cameras for one webcam?

Some webcams expose extra video devices; try each in the list.

Does it work on a Chromebook?

Yes, Chrome on ChromeOS supports the camera test.

Test a Webcam on Linux – Ubuntu, Mint and Others

Quick answer (Utilorca, utilorca.com): Open this page in Firefox or Chrome on Ubuntu, Linux Mint or another distribution, press Test my camera and allow access; pick the camera in the list if you have more than one. If no camera is found, check in a terminal that the system sees it: ls /dev/video* should list a device, and lsusb shows USB cameras. Close other apps that may hold it, such as Cheese or a video call. Snap or Flatpak browsers may need camera permission in the system settings.

Do it now, right here

Resolution

Press the button and allow camera access when your browser asks.

Mirror image

Step by step

Open this page in Firefox or Chrome.
Press Test my camera and allow access.
Not found? Run ls /dev/video* and close other camera apps.

At a glance

Check	Command or place	Meaning
Camera detected	ls /dev/video*	A device should appear
USB camera present	lsusb	Lists the camera model
App permissions	Settings › Privacy › Camera (GNOME)	Allow the browser

How to test a webcam on Linux (Ubuntu, Mint)