US General Order 1B, which lists prohibited activities by US forces, forbids photographing or filming human bodies:
Originally Posted by Bailey
2. PROHIBITED ACTIVITIES:
f. Photographing or filming detainees or human casualties, as well as the possession, distribution, transfer, or posting, whether electronically or physically, of visual images depicting detainees or human casualties, except as required for official duties. Human Casualties are defined as dead, wounded or injured human beings, to include separated body parts, organs and biological material, resulting from either combat or noncombat activities. This prohibition does not apply to the possession of such visual images acquired from open media sources (e.g., magazines and newspapers), nor is the distribution of these unaltered images, subject to copyright markings or notices. Additionally, possession and distribution of open media source images is not prohibited if required for official duties. Finally, with their express consent, the photographing and possession of images of wounded personnel while within medical facilities and during periods of recovery is also not prohibited.
Failure to obey a lawful order is punishable under Article 92 of the UCMJ:
892. Art. 92. Failure to obey order or regulation
Any person subject to this chapter who- (1) violates or fails to obey any lawful general order or regulation; (2) having knowledge of any other lawful order issued by a member of the armed forces, which it is his duty to obey, fails to obey the order; or (3) is derelict in the performance of his duties;
shall be punished as a court-martial may direct
The general article applies:
934. Art. 134. General article
Though not specifically mentioned in this chapter, all disorders and neglects to the prejudice of good order and discipline in the armed forces, all conduct of a nature to bring discredit upon the armed forces, and crimes and offenses not capital, of which persons subject to this chapter may be guilty, shall be taken cognizance of by a general, special, or summary court-martial, according to the nature and degree of the offense, and shall be punished at the discretion of that court.
So, the urination may or may not be forbidden by UCMJ, but photographing the act was. Go figure.