I ran some pictures through a celebrity look-a-like program, and here are the results for this photo:

Results below; bold is the one that was declared the best match by the program used. Others are just other matches that I found funny.
Nathan (bottom left)=Angelina Jolie, Billy Idol
Isaac (top left)=Leslie Caron, Shirley Temple
Me (bottom middle)=Kate Beckinsale, Quentin Tarantino, Billie Piper, Alyson Hannigan
Derek (top middle)=Matthew Lillard
Noah (top right)=Matt Stone
Karl (bottom right)=Billie Piper, Harry Houdini
I chose the names for the ones I found funny because of the fact that they were some of the few I knew, and/or I LOVED THEM! For those who are interested, full lists can be seen by clicking the link to read on.
This got me thinking; what do they use to compare?. After a couple of tests I figured it out. They scan the picture for places that look like they have two eyes, a nose, and a mouth. If you've got eyes, nose, lips, cheek bones, blah blah blah, in the same place as this photo they have, then BAM! You're a shoe-in! So, it's about the positioning of the face and camera. Huh.
Nathan
Angelina Jolie (80%)
Kim Novak (76%)
Krista Allen (76%)
Carole Lombard (75%)
Billy Idol (72%)
Shlomo Artzi (71%)
Amisha Patel (68%)
Katherine Hepburn (68%)
Rose McGowan (67%)
Keanu Reeves (67%)
Isaac
Leslie Caron (63%)
Fernanda Tavares (63%)
Queen Latifah (60%)
Kylie Bax (59%)
Carrie-Anne Moss (59%)
Stacy Keibler (58%)
Sharon Stone (57%)
Shirley Temple (56%)
Simon (me)
Kate Beckinsale (73%)
Quentin Tarantino (68%)
Nicky Hilton (66%)
Billie Piper (64%)
Jack Dempsey (63%)
Vanessa Marcil (63%)
Brian Littrell (61%)
Alyson Hannigan (59%)
Katie Holmes (59%)
Howie Day (59%)
Derek
Matthew Lillard (59%)
Janeane Garofalo (59%)
Gwyneth Paltrow (51%)
Jesse L. Martin (47%)
Kim Rae Won (47%)
Cristiano Ronaldo (46%)
Noah
Matt Stone (66%)
Salma Hayek (64%)
Penelope Cruz (64%)
Estella Warren (60%)
Lucille Ball (59%)
Allan Kardec (58%)
Frida Kahlo (57%)
Jennifer Love Hewitt (56%)
Aidan Quinn (56%)
Romy Schneider (56%)
Karl
Billie Piper (75%)
Gemma Ward (72%)
Kim Hee-sun (70%)
Harry Houdini (66%)
Krista Allen (64%)
Alicia Keys (63%)
Carole Lombard (63%)
Coco Chanel (63%)
Ali Landry (62%)
Liya Kebede (62%)
It strikes me interesting that Karl's top match was my fourth. I'd also like to note that Derek started at 59%, where I ended. Some people just have those faces and some don't, I guess.
Thus ends my study.