From Google
http://www.google.com/support/bin/answer.py?answer=630&ctx=sibling&topic=360
Concerns About Content in Our Index: An image
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It may be that Google doesn't want to present images of official documents that could be used for making forgeries. Maybe even that State of Hawaii or Homeland Security have asked them to do so. I do not know.
Because Google has not kept it's hands balanced left-vs-right in the past, the deletion of the images as it acts to repress the investigation by citizens for themselves of the issue is reasonably suspicious as being in motive an effective political knee-capping of Obama's opponents.
And just like the questions as do why Obama isn't clarifying the matter of his BC raise issues of his openess and honesty, so to does this event on the part of Google. Both issues could easily be resolved by public openess, by a reasoned and complete explanation that would withstand some scrutiny and due diligence.
Yahoo Image search is also scrubbed. You can pull up “birth certifciates” and get birth certificate images but neither “obama birth certificate” nor “decosta birth certificate” return images of certificates. Other names besides those two — such as allen, smith — returned some certificate images, both for Google and Yahoo.