Create a placeholder picture.

placeholder.py

#!/usr/bin/env python

from tornado.web import Application, RequestHandler
from tornado.ioloop import IOLoop
from PIL import Image, ImageDraw, ImageFont, ImageColor
import cStringIO
import re

fontPath = '/Library/Fonts/Arial.ttf'
port = 8080

def createImg(width, height, color, text, format):
    img = Image.new('RGBA', (width, height), color)
    draw = ImageDraw.Draw(img)
    fontSize = 32
    while True:
        font = ImageFont.truetype(fontPath, fontSize)
        textWidth, textHeight = draw.textsize(text, font=font)
        if textWidth > width or textHeight > height:
            fontSize /= 2
        else:
            break
    textLeft = (width - textWidth) / 2
    textTop = (height - textHeight) / 2
    textColor = 'White' if sum(ImageColor.getrgb(color)) < 255 * 3 / 2 else 'Black'
    draw.text((textLeft, textTop), text, font=font, fill=textColor)
    fim = cStringIO.StringIO()
    img.save(fim, format)
    binData = fim.getvalue()
    fim.close()
    return binData


class IndexHandler(RequestHandler):
    def get(self):
        sizeArg = self.get_argument('size', '512x512')
        sizeMatch = re.match(r'(\d+)[xX](\d+)', sizeArg)
        width = int(sizeMatch.group(1))
        height = int(sizeMatch.group(2))
        color = self.get_argument('color', 'gray')
        try:
            int(color, 16)
            color = '#' + color
        except ValueError:
            pass
        text = self.get_argument('text', '%s * %s' % (width, height))
        img = createImg(width, height, color, text, 'PNG')
        self.set_header('content-type', 'image/png')
        self.set_header('content-length', len(img))
        self.write(img)

appSettings = {
    'debug': True,
}
application = Application([
    ('/', IndexHandler),
], **appSettings)
        
if __name__ == '__main__':
    application.listen(port)
    IOLoop.instance().start()