Well, Amy and her siblings posed for this photo, but Peter was not there. So, Peter is not in the photo. Because he was not there.
This photo was taken in 1904, and the card was written by Amy. It seems that the fact that 'Peter' was not included in the group was something that mattered to her. Peter, I am assuming, was an older brother? He was working in the field when the photo was taken. But, since the image is clear, you will be able to read the entire note too!