Tweeting Letterbox. Blog post: http://jamesmedd.tumblr.com/post/35270913619/raspberry-pi-tweeting-letterbox

tweeting_letterbox.py

# Tweeting Letterbox
# by James Medd
# November 2012 (original version)
# http://jamesmedd.co.uk/

#!/usr/bin/python 

import picamera
import RPi.GPIO as GPIO
import sys
import time
from twython import Twython

#OAuth details go here
CONSUMER_KEY = ""
CONSUMER_SECRET = ""
ACCESS_TOKEN = ""
ACCESS_TOKEN_SECRET = ""

#initialise Camera
camera = picamera.PiCamera()

#set input GPIO pin
GPIO.setmode(GPIO.BOARD)
GPIO.setup(11, GPIO.IN)

twit = Twython(CONSUMER_KEY, CONSUMER_SECRET, ACCESS_TOKEN, ACCESS_TOKEN_SECRET)

#timestamp, capture, and tweet an image
def capture_tweet():	
	timestamp = time.strftime("%d%m%Y-%H%M%S")
	camera.capture(timestamp + ".jpg") #save image to disk
	image = open(timestamp + ".jpg", 'rb')
	timestamp = "@Username " + timestamp
	twit.update_status_with_media(status=timestamp, media=image)
	print "Tweeted image at " + timestamp #make a record in the Python output

#try/except for tidy starting/stopping of script
try:
	print "Tweeting Letterbox initialised. Exit using Ctrl + c."
	#loop to check PIR state/trigger a tweet (exit using Ctrl+C)
	while True:
		ir_val = GPIO.input(11)
		if not ir_val:
			time.sleep(0.5) #wait before checking again if nothing detected
		elif ir_val:
			capture_tweet() #capture and tweet image if triggered
			while ir_val:
				ir_val = GPIO.input(11)
				time.sleep(0.5) #wait for sensor to reset/movement to stop before checking again
		else:
			print "Error"
except KeyboardInterrupt:
	print "\nExiting.",
	sys.exit()

Added an update to use the Raspberry Pi Camera module instead of a webcam. Also updated Twython-related code in line with their documentation guidelines etc.