DNA says so much in a single picture. First, getting students to have an idea of what x-ray crystallography IS can be difficult. They have been seeing this odd black and white picture in chapters on DNA in their textbooks since high school, so it obviously has a biology connection.
Second, it connects the importance of the contribution of women in science. Rosalind Franklin not only discerned that the phosphate backbone was on the OUTSIDE of the structure, she also was among the first to crystallize the B form of DNA, which created clearer x-ray diffraction patterns and is more biologically relevant.
Finally, though it is well known, DNA is far from a cliche molecule. Its versatility and stability fascinate biologists, chemists, engineers, and physicists. Every field has a niche for it.
I am certain you will get this answer often, and for the best of reasons — while we have beautiful structures of many things of importance, you will find it difficult to find a scientist (amateur to professional) who is unfamiliar with the beauty of their own legacy and lineage: DNA. —Stephanie Taylor