To use a webcam with ROS, I do the following:

mkdir -p ~/catkin-ws/src

$ cd ~/catkin-ws/src

 git clone https://github.com/ros-drivers/usb_cam
cd ..
catkin_make

For this last line, depending on your catkin tools installation, you might need to run catkin build instead. This is,

catkin build

Finally do,

$ source ~/catkin-ws/devel/setup.bash

Then connect the camera and run the following launch file.

usb_cam-test.launch

You should see a window with the image now.  I tested this with my webcam Odroid HD 720P.

Good luck!