21 years a family Jun 25 2014
Beginning in 1991, Zed Nelson took a photo of the same family (father, mother, and son) in front of the same backdrop every year for 21 years. Here's the first photo:
And the most recent one:
There are many more such projects, including the Goldberg family's annual portraits, Nicholas Nixon's annual portraits of The Brown Sisters, and Noah Kalina's Everyday.