A good picture lends power to documentation. Even before I look at the document that accompanies an experience, I turn to the picture to tell me the story, to identify the learning, to make the connection, to show the child's emotions, interests and expressed theories.
Digital cameras allow you to take many photos so snap away. When you have a quiet moment you can select the ones that demonstrate the process best.
Group pictures are equally as important in the constructing and deconstructing of theories. This is especially true with older children where much happens in group discourse and work.