I believe the vcgencmd only refers to the videocore connected cameras - i.e. Raspberry Pi Camera Interface (CSI) cameras. If you are using a USB camera (e.g. webcam), then that is completely different.

- Gough

USB Webcams are probably done through v4l, try sudo with the fswebcam command.

Maybe you are right.

I use the command $fswebcam /dev/video0 ~/image.jpg

I can get a image.jpg in the /home/pi

but when I input the command $sudo raspistill -o camera.jpg, I still get

mmal: Cannot read camera info, keeping the default for OV5647

mmal: mmal_vc_component_create: failed to create component 'vc.ril.camera' (1:ENOMEM)

mmal: mmal_vc_component_create_core: could not create component 'vc.ril.camera' (1)

mmal: Failed to create camera component

mmal: main: Failed to create camera component

mmal: Camera is not detected. Please check carefully the camera module is installled correctly

Why? Just because my camera is USB not CSI？

raspistill is designed for use with the camera module only - it's not for use with v4l devices or uvc devices.

See the first line of https://www.raspberrypi.org/documentation/usage/camera/raspicam/raspistill.md

raspistill

raspistill is the command line tool for capturing still photographs with the camera module.

Thanks very much for your answer.

I created a CameraTest.py file

form picamera import PiCamera

fome time import sleep

camera=Picamera()

camera.start_preview()

camera.capture('home/pi/image.jpg')

camera.stop_preview()

when I run, the error appears

mmal: mmal_vc_component_create: failed to create component 'vc.ril.camera' (1:ENOMEM)

mmal: mmal_vc_component_create_core: could not create component 'vc.ril.camera' (1)

I think maybe the reason is the same "designed for use with the camera module only - it's not for use with v4l devices or uvc devices".

But how can I use .py file to control USB camera?

Perhaps you could do a little googling to find what you need - as I mentioned, most of the Pi camera tools are for the Raspberry Pi Camera Module and not just any random USB-Video Class device like a webcam.

Perhaps try using OpenCV's cv2:

https://stackoverflow.com/questions/604749/how-do-i-access-my-webcam-in-python

- Gough

You don't have a "pi camera", so the "picamera" module in python doesn't work. It does the equivalent of "raspistill" that you found out doesn't work.

Thank you, Gough.

I decide to buy a csi camera to test whether I can use command raspistill.

And I write a CameraTest2.py file according the reference from "https://blog.csdn.net/HANNING563128766/article/details/80033498 "

import pygame

import pygame.camera

from pygame.locals import *

pygame.init()

pygame.camera.init()

camera = pygame.camera.Camera("/dev/video0",(640,480))

camera.start()

image = camera.get_image()

pygame.image.save(image,"image.jpg")

camera.stop()

When I run, I get a image.jpg in the same folder of CameraTest2.py