to reproduce Google image pending.
Each search engine uses software (called spiders
or robots) to compile a database of pages
found on the publicly accessible Web. When you enter
a search, the search engine scans its own database
of Web pages for the keywords you enter, wherever
they appear on a Web page.
So, each search engine searches only the part of the
Web it has collected and each search engine has a
somewhat different database.
Other search engines include: Bing, HotBot, and Teoma.