Watson and Crick obtained the photograph that was taken by Rosalind Franklin through a scientific colleague, Maurice Wilkins, who was working with Franklin at the time. Franklin was using X-ray crystallography to study the structure of DNA, and Wilkins showed Watson and Crick one of her photographs, known as Photograph 51, without her knowledge or consent.
Photograph 51 was important because it provided key information about the structure of DNA that was crucial to Watson and Crick's discovery of the double helix structure of DNA. The photograph showed clear X-ray diffraction patterns, indicating that DNA fibers had a regular, repeating structure. By analyzing the pattern of the diffraction, Watson and Crick were able to determine the basic structure of the DNA molecule and propose the double helix model.