title: Cannot download image with relative URL Python Scrapy
body: <p>I'm using Scrapy to download images from <a href="http://www.vesselfinder.com/vessels" rel="nofollow">http://www.vesselfinder.com/vessels</a></p>
  
  <p>However, I can only get the relative url of images like this <a href="http://www.vesselfinder.com/vessels/ship-photo/0-227349190-7c01e2b3a7a5078ea94fff9a0f862f8a/0." rel="nofollow">http://www.vesselfinder.com/vessels/ship-photo/0-227349190-7c01e2b3a7a5078ea94fff9a0f862f8a/0</a> </p>
  
  <p>All of the image named 0.jpg but if I try to use that absolute url, I cannot get access to the image.</p>
  
  <p>My code:
  <strong>items.py</strong></p>
  
  <pre><code>import scrapy
  
  class VesselItem(scrapy.Item):
      name = scrapy.Field()
      nationality = scrapy.Field()
      image_urls = scrapy.Field()
      images = scrapy.Field()
  </code></pre>
  
  <p><strong>pipelines.py</strong></p>
  
  <pre><code>import scrapy
  from scrapy.contrib.pipeline.images import ImagesPipeline
  from scrapy.exceptions import DropItem
  
  class VesselPipeline(object):
      def get_media_requests(self, item, info):
          for image_url in item['image_urls']:
              yield scrapy.Request(image_url)
  
      def item_completed(self, results, item, info):
          image_paths = [x['path'] for ok, x in results if ok]
          if not image_paths:
              raise DropItem("Item contains no images")
          item['image_paths'] = image_paths
          return item
  </code></pre>
  
  <p><strong>vessel_spider.py</strong></p>
  
  <pre><code>import scrapy
  import string
  
  from vessel.items import VesselItem
  
  class VesselSpider(scrapy.Spider):
      """docstring for VesselSpider"""
      name = "vessel"
      allowed_domains = ["vesselfinder.com"]
      page_name = "http://vesselfinder.com"
      start_urls = [
          # "http://vesselfinder.com/vessels?page=%d" %i for i in range(0,1000)
          "http://vesselfinder.com/vessels"
      ]
  
      def parse(self, response):
          f = open('vessels.txt', 'a')
          count = 0;
  
          for sel in response.xpath('//div[@class="items"]/article'):
              item = VesselItem()
  
              imageStr = str(sel.xpath('div[1]/a/picture/img/@src').extract())
              item['image_urls'] = self.page_name + imageStr[3:-2]
              nameStr = str(sel.xpath('div[2]/header/h1/a/text()').extract())
              item['name'] = nameStr[19:-8]
              typeStr = str(sel.xpath('div[2]/div[2]/div[2]/text()').extract())
              item['type'] = typeStr[3:-2]
  
              return item
  </code></pre>
  
  <p>When I run this spider, I got the <code>exceptions.ValueError: Missing scheme in request url: h</code> error because I did not provide the absolute url.</p>
  
  <pre><code>[vessel] ERROR: Error processing {'image_urls': 'http://vesselfinder.com/vessels/ship-photo/0-224138470-a2fdc783d05a019d00ad9db0cef322f7/0.jpg',
       'name': 'XILGARO ALEANTE',
       'type': 'Sailing vessel'}
      Traceback (most recent call last):
        File "/usr/local/lib/python2.7/dist-packages/scrapy/middleware.py", line 62, in _process_chain
          return process_chain(self.methods[methodname], obj, *args)
        File "/usr/local/lib/python2.7/dist-packages/scrapy/utils/defer.py", line 65, in process_chain
          d.callback(input)
        File "/usr/local/lib/python2.7/dist-packages/twisted/internet/defer.py", line 383, in callback
          self._startRunCallbacks(result)
        File "/usr/local/lib/python2.7/dist-packages/twisted/internet/defer.py", line 491, in _startRunCallbacks
          self._runCallbacks()
      --- &lt;exception caught here&gt; ---
        File "/usr/local/lib/python2.7/dist-packages/twisted/internet/defer.py", line 578, in _runCallbacks
          current.result = callback(current.result, *args, **kw)
        File "/usr/local/lib/python2.7/dist-packages/scrapy/contrib/pipeline/media.py", line 40, in process_item
          requests = arg_to_iter(self.get_media_requests(item, info))
        File "/usr/local/lib/python2.7/dist-packages/scrapy/contrib/pipeline/images.py", line 104, in get_media_requests
          return [Request(x) for x in item.get(self.IMAGES_URLS_FIELD, [])]
        File "/usr/local/lib/python2.7/dist-packages/scrapy/http/request/__init__.py", line 26, in __init__
          self._set_url(url)
        File "/usr/local/lib/python2.7/dist-packages/scrapy/http/request/__init__.py", line 61, in _set_url
          raise ValueError('Missing scheme in request url: %s' % self._url)
      exceptions.ValueError: Missing scheme in request url: h
  </code></pre>
  
  <p>How should I fix this. Is there any special way for getting image (or its absolute url) with the site like this one.</p>