[enh] image proxification

searx/settings.yml

     default_theme : oscar # ui theme
     https_rewrite : True # Force rewrite result urls. See searx/https_rewrite.py
     useragent_suffix : "" # suffix of searx_useragent, could contain informations like an email address to the administrator
+    image_proxy : False # Proxying image results through searx
 
 engines:
   - name : wikipedia

searx/webapp.py

 from datetime import datetime, timedelta
 from requests import get as http_get
 from itertools import chain
+from urllib import urlencode
 from flask import (
     Flask, request, render_template, url_for, Response, make_response,
     redirect, send_from_directory
     return url_for(endpoint, **values)
 
 
+def image_proxify(url):
+
+    if url.startswith('//'):
+        url = 'https:' + url
+
+    if not settings['server'].get('image_proxy') and not request.cookies.get('image_proxy'):
+        return url
+
+    return '{0}?{1}'.format(url_for('image_proxy'),
+                            urlencode(dict(url=url)))
+
+
 def render(template_name, override_theme=None, **kwargs):
     blocked_engines = request.cookies.get('blocked_engines', '').split(',')
 
     # override url_for function in templates
     kwargs['url_for'] = url_for_theme
 
+    kwargs['image_proxify'] = image_proxify
+
     kwargs['get_result_template'] = get_result_template
 
     kwargs['theme'] = get_current_theme_name(override=override_theme)