Note: I found the above books by browsing by subject ("Radiology") in both AccessMed and ClinicalKey. Neither database allowed me to search for the term "x-ray".
Citing an image found in an ebook.
In Vancouver Style:
The Urbana atlas of pathology [Internet]. Urbana (IL): University of Illinois College of Medicine at Urbana-Champaign; c1994-1997. Image No. 034, Left ventricular hypertrophy, heart; [cited 2006 Nov 15]; [about 1 screen]. Available from: http://www.med.uiuc.edu/PathAtlasf/CVAtlas034.html
Citing an image found in an image database like VisualDX or AnatomyTV.
Caption below image: "Image source: VisualDX"
Citation at end of presentation/paper:
AnatomyTV [Internet]. London: Informa PLC, Primal Pictures. Copyright 2016 - . [Image], Neurovasculature of the spinal cord: anterior aspect; [cited 20 July 2016]; [about 1 screen]. Available from: http://anatomy.tv/GotoView.aspx?productname=interactivespine2014&modelID=-1&mediaID=9518282&structureID=-1&mediaTypeID=4&productID=452.
Medpix [Internet]. Bethesda (MD): National Library of Medicine (US). [date unknown] - . [Image], Acute ischemic stroke: Hyperacture stroke, left-sided paresis and hemineglect; [cited 20 July 2016]; [about 1 screen]. Available from https://medpix.nlm.nih.gov/case?id=88854bc4-688b-4f39-acdf-4b534bdb2596.