The yearbook photo is the most important pictures a teenager takes. (Some teen stars whose less-formal pics have leaked to the Web might disagree.) More so than any snapshot tagged on Facebook, or even that lovely pic taken at the DMV, the yearbook portrait is the picture that will define your high school experience for decades to come, whether you like it or not.

It is not surprising, then, that celebrities' yearbook photos have always been a pop-culture curiosity. Learning that Brad Pitt was a skinny dweeb in high school, for example, makes other skinny dweebs feel like they could turn into the Sexiest Man Alive, earn a zillion dollars, marry a hot lady and adopt half of Africa too! There's something really comforting in knowing that back before they had 'round-the-clock stylists and makeup artists, celebrities looked just like us, warts and all.

We've tracked down some of our favorite current celebrities and analyzed their high school portraits to get a little insight into where they came from.

(Check out our [article id="1614205"]favorite celebrity yearbook photos[/article] here.)

[url id="http://www.mtv.com/photos/meet-the-class-of-09/1614205/3985713/photo.jhtml"]Adam Lambert[/url] wasn't always the glamazon rocker we met on "American Idol." Back in his high school days, he was a healthy-looking strawberry-blond theater geek who liked sleeping in class. Perhaps he was dreaming about performing with Kiss while wearing an outfit from the Thunderdome.

[url id="http://www.mtv.com/photos/meet-the-class-of-09/1614205/3985708/photo.jhtml"]Megan Fox's[/url] sophomore portrait will likely make girls hate her even more. Yep, she's always been that smoking hot. And thanks to the classic framing of a school photo, her funky thumbs are nowhere to be found.

By the time [url id="http://www.mtv.com/photos/meet-the-class-of-09/1614205/3985705/photo.jhtml"]Tyra Banks[/url] graduated from high school, she had already traveled the world for her modeling career, so it's shocking that TyTy's photo is 40 percent less fierce than one would expect. On "America's Next Top Model," Queen Tyra is always chewing out girls for looking more like actresses than models. If only modern-day Tyra could time-travel back to teach high school Tyra a lesson.

[url id="http://www.mtv.com/photos/meet-the-class-of-09/1614205/3985712/photo.jhtml"]Fergie[/url] was also a child star, having headlined the cheesy series "Kids Incorporated" in her younger days. By the time she was a senior, she was g-l-a-m-o-r-o-u-s, and showed a lot of c-l-e-a-v-a-g-e in her senior portrait. Is that flossy flossy or tacky tacky?

You learn a lot about Kate Kreider (who would eventually grow up to become reality-TV star/ tabloid-cover staple [url id="http://www.mtv.com/photos/meet-the-class-of-09/1614205/3985710/photo.jhtml"]Kate Gosselin[/url]) by looking at her yearbook. A blurb about the then-senior reveals that she disliked the Friendly's food chain (why?!), her nicknames were "Bruise" and, uh, "Bruce," and she had lots of signature quotations, such as "Uh, I hated that!" "I need a nap!" "Not today" and "I love it." (It doesn't mention whether she was really good at rolling her eyes and being passive-aggressive, though. Perhaps those are skills she picked up later in life?) The most interesting quote, however, is, "Aww Jonny, you're SO cute!" If she only knew...

Speaking of reality stars, [url id="http://www.mtv.com/photos/meet-the-class-of-09/1614205/3985707/photo.jhtml"]Spencer Pratt's[/url] sophomore pic is quite telling. Even back then, he was connected at the hip with a vacant-looking blonde. Some things never change.

And finally, "Twilight" author [url id="http://www.mtv.com/photos/meet-the-class-of-09/1614205/3985706/photo.jhtml"]Stephanie Meyer[/url] (or, as her classmates knew her, Stephanie Morgan) looked like your average teenage bookworm. And for a girl who was in love with a vampire, her skin tone is pretty rosy. ("Twilight" is an autobiography, right?)

Congratulations to the Class of '09. Our advice to the future leaders of the world? Hold on to your yearbooks. You never know which one of your classmates will become the next big thing.

It's Class of '09 Week on MTVNews.com, where we're celebrating a memorable time in the lives of more than 3 million high school seniors: graduation! We're rolling out articles and videos with graduation memories from your favorite celebrities and much more. Be sure to upload your own three-minute video for our Class of '09 Valedictory Search to Your.MTV.com -- the winner will be flown to New York for lunch with MTV News' Sway and will attend a taping of MTV's new series "It's On With Alexa Chung."