I saw this on Israeli Insider. Don’t know if it is true or not; but sounds like it has merit:
http://web.israelinsider.com/Articles/Politics/12993.htm
In the comments by a poster named muzhik:
Obama may never have had to produce his birth certificate to get a passport. As a baby, he would have been included in his mother’s passport as a “family passport”. Whoever took her application may not have required her baby’s BC — it’s the ‘60s, she’s white, the daddy’s black, and it’s not like the kid will ever run for president. Sloppy by today’s standards, but not necessarily by the standards of the time.
After that, it’s just a matter of keeping the passport renewed. When he turned 14, Obama would have gotten his own passport, using the “family” passport as proof of citizenship. If he kept his passport renewed, he never would have needed to produce a certified birth certificate.
And probably the same with his Kenyan and Indonesian passports one of which he likely used on his recently revealed trip to Pakistan.