From the notes at the Ransom Center at the University of Texas (a few more images there):
"Danh has pioneered a fascinating mode of printing directly on plant leaves through the natural process of photosynthesis. By placing a negative in contact with a living leaf and then exposing it to sunlight for several weeks, the image literally becomes part of the leaf. Danh then permanently “fixes” the image by casting it in resin. He calls the finished piece a “cholorophyll print.” These compelling objects appear very contemporary, but also harken back to the botanical photogenic drawings created by William Henry Fox Talbot at the dawn of photography....
Images from the Vietnam War are prevalent in his work, providing a unique connection between process and subject matter. As he explains, "This processdeals with the idea of elemental transmigration: the decomposition and composition of matter into other forms. The images of war are part of the leaves, and live inside and outside of them. The leaves express the continuum of the war. They contain the residue of the Vietnam War: bombs, blood, sweat, tears, and metals. The dead have been incorporated into the landscape of the Vietnam during the cycles of birth, life, and death, through the recycling and transformation of materials, and the creation of new materials."
(my "advisor" thinks they are a little bit too contrived, but on the whole I disagree...)
and a piece on NPR