The PhotoId can be used to create an image url with a specific size.
* Format
SCALED images are scaled to have a height and width no larger than the size
specified while maintaining the aspect ratio of the original image. If the original
image was smaller than the pixels specified then the image is not changed at all
from the original (i.e. it will be smaller than the size specified).
SQUARED images always have the height and width specified. The images are
cropped to fit inside a square. If the original image is smaller than the size specified
the image is "blown-up" so that it fits the square.