pipelines.py

from scrapy.contrib.pipeline.images import ImagesPipeline
from scrapy.exceptions import DropItem
from scrapy.http import Request

class MyImagesPipeline(ImagesPipeline):

    def get_media_requests(self, item, info):
        for image_url in item['image_urls']:
            yield 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
    def process_item(self, item, spider):
        if spider.name == 'vinNico3':
            print "inside process_item"
#class Projetvinnicolas3Pipeline(object):
#    def process_item(self, item, spider):
#       return item

You have to call the superclass' method and return its result
otherwise you are discarding all items

    def process_item(self, item, spider):
        if spider.name == 'vinNico3':
            print "inside process_item"
        return super(MyImagesPipeline, self).process_item(item, spider)

You can also NOT define the method.