Dave Eggers uses pictures and emails to personalize the character Zeitoun. While Zeitoun is a real person, it's better to treat him as a character Eggers creates.
In the post-9/11 world, there is a certain instant stereotype pinned on AV Muslim man, which is that of a radical. Throughout the book, Eggers does his best to portray Abdulrahman as someone a community should be happy to welcome, something that isn't always the case for Muslims in America. So, the photos of him smiling or of him hugging his kids helps counter the radical Muslim stereotype.
The emails, meanwhile, show the care others have for Zeitoun. Ahmed, Abdulrahman's brother, emails anyone who might be able to help. These actual emails show the length with which others attemp to help this man. Again, this type of concern runs contrary to stereotypes.
A second reason to include emails in the story is that they give more credence to the worldwide concern for Zeitoun and the worldwide attention given to the aftermath of Hurricane Katrina.