14. A method performed by a search engine service, the method comprising: receiving, at a search engine server from an end user computing device, a plurality of content signatures signature of a web page, the plurality of content signatures signature having been automatically generated at the end user computing device from content of the web page downloaded and displayed by the end user computing device, the web page having been downloaded by the end user user's computing device from one or more content servers separate from the search engine server when an end user employed the end user computing device to access the web page during a web browsing session, each content signature corresponding with a different portion of the content of the web page, each portion comprising one of text, images, video, and audio; analyzing, at the search engine server, the plurality of content signatures signature to identify a portion of the content that has changed on the change in the content of the web page by determining a difference between at least one of the plurality of content signatures and a content signature accessible by the search engine server the content signature and a second content signature of the web page accessible by the search engine server; and controlling crawling of the web page by the search engine server based on the portion of the content that has changed on the web page identifying the change in the content of the web page.
17. The method of claim 14 , wherein analyzing the plurality of content signatures comprises determining an extent to which the content of the web page has pages have changed.