This is my setting:
Arduino UNO is connected over USB to my computer, I am using SoftwareSerial. PIN 4 is connected to TX, PIN 5 to RX, GND is connected to GND on the board of a webcam (7links robocam PX3309). I did not connect +5V on webcam side to +5V of the arduino, as the +5V is already powering the Webcam.