Requires USB HID Firmware which can be found at http://mitchtech.net/arduino-usb-hid-keyboard/ Works with Webcam Photobooth. When button1 is pushed it sends ctrl+p & F3 which triggers color photo taking. When button2 is pushed it sends ctrl+v & f7 which triggers video

PhotoboothButton.ino

#define KEY_LEFT_CTRL  0x01
#define KEY_LEFT_SHIFT	0x02
#define KEY_RIGHT_CTRL	0x10
#define KEY_RIGHT_SHIFT	0x20

const int button1Pin = 2;
const int button2Pin = 7;
const int ledPin = 13;

// Keycode 60 is F3. 
// See page 55 for more http://www.usb.org/developers/devclass_docs/Hut1_11.pdf
const int f3KeyboardCode = 60;
const int f7KeyboardCode = 64;
const int vKeyboardCode = 25;
const int pKeyboardCode = 19;

int buttonState = 0; 

uint8_t buf[8] = { 
  0 };
  
void setup() {
  Serial.begin(9600);
  // initialize the LED pin as an output:
  pinMode(ledPin, OUTPUT);      
  // initialize the pushbutton pin as an input:
  pinMode(button1Pin, INPUT); 
  pinMode(button2Pin, INPUT);    
}

void loop() {

  if(readButton(button1Pin, f3KeyboardCode, pKeyboardCode))
  {
  }
  else if(readButton(button2Pin, f7KeyboardCode, vKeyboardCode))
  {   
  }
  else
  {
    digitalWrite(ledPin, LOW); 
    keyOff();
  }
}


boolean readButton(int pin, int keyboardCode, int switchModeCode)
{
     // read the state of the pushbutton value:
  buttonState = digitalRead(pin);

  // check if the pushbutton is pressed.
  // if it is, the buttonState is HIGH:
  if (buttonState == HIGH) {     
    // turn LED on:    
    digitalWrite(ledPin, HIGH);  
    keyOn(keyboardCode, switchModeCode);
    
    return true;
  }
  
  return false;
}

void keyOn(int keyboardCode, int switchModeCode)
{
  buf[0] = KEY_LEFT_CTRL;
  buf[2] = switchModeCode;
  Serial.write(buf, 8);
  delay(10);
  
  keyOff();
  
  buf[2] = keyboardCode;
  Serial.write(buf, 8);
}

void keyOff()
{
  buf[0] = 0;
  buf[2] = 0;
  Serial.write(buf, 8);
}

Wiring diagram is from the button tutorial http://arduino.cc/en/tutorial/button