camera status warn,image status warn

Hello everyone I am using Artags alvar but when I use command "rosrun rviz rviz -d rviz_artag_config.rviz" I get window but with Camera Status warn,Image status Warn no image captured by camera. I use camera usb logitech.Could you inform me what should I do now Thanks in advance Best Taher ---------- EDIT Hello I am using Logitech camera by `using usb_camera usb_camera.launch` file But I get error in Camera Calibration Waiting for service', '//set_camera_info,Service not found. and now in visualizing the Ar_tags_alvar.I sucessfully build alvar and using ROS_indigo packages. Best Taher