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REPORT OF COMMISSION VII 
FIG. 4. DEFINITIONS RELATIVE TO PHOTO-INTERPRETATION KEYS, PROPOSED 
BY THE INTERSERVICE COMMITTEE ON PHOTO-INTERPRETATION 
RESEARCH, KEYS, AND TECHNIQUES. 
A photo interpretation key is reference material designed to facilitate rapid and accurate 
identification and determination of the significance of objects or conditions from the analysis 
of their photo images. Ideally, the key consists of two parts; (a) a collection of annotated 
or captioned stereograms and other photos which are illustrative of the objects or conditions 
to be identified and (b) a graphic or word description which sets forth in some systematic 
‘fashion the photo recognition features of those objects or conditions. 
Photo interpretation keys may be classified as to scope, technical level, intrinsic 
character, and manner of organization or presentation. Each of the following definitions 
is based upon the fundamental definition of a photo interpretation key, stated above. 
1. SCOPE OF PHOTO INTERPRETATION KEYS 
a. An item key is one concerned with the identification of an individual object or 
condition. 
b. A subject key is a collection of item keys concerned with the principal objects 
or conditions within a given subject category. 
c. A regional key is a collection of item or subject keys concerned with the 
identification of the principal objects or conditions characteristic of a particular region. 
d. An analogous area key is a subject or regional key which has been prepared for 
an accessible area end which by extrapolation may be used in the interpretation of objects 
or conditions in inaccessible areas having similar characteristics. 
2. TECHNICAL LEVEL OF PHOTO INTERPRETATION KEYS 
a. A technical key is one prepared primarily for use by photo interpreters who have 
had professional or technical training or experience in the subject concerned. 
b. A non-technical key is one prepared primarily for use by photo interpreters who 
have not had professionel or technical training or experience in the subject concerned. 
3. INTRINSIC CHARACTER OF PHOTO INTERPRETATION KEYS 
a. A direct key is one designed primarily for the identification of discrete objects 
or conditions directly discernible on photos. 
b. An associative key is one designed primarily for the deduction of information not 
directly discernible on photos. 
hl. MANNER OF ORGANIZATION OR PRESENTATION OF PHOTO INTERPRETATION KEYS ; 
All photo interpretation keys are based upon diagnostic features of the photo images 
of objects or conditions to be identified. Depending upon the manner in which the diagnostic 
features are organized, two general types of keys are recognized: "Selective keys" are so 
arranged that the photo interpreter simply selects that example corresponding to the image he 
is trying to identify. "Elimination keys" are so arranged that the photo interpreter follows 
a prescribed step-by-step process that leads to the elimination of all items except the one he 
is trying to identify. Where feasible of formulation the latter type of key is considered preferable. 
a. Selective keys 
(1) An essay key is one in which the objects or conditions are described in 
textual form using photos only as incidental illustrations. 
(2) A file key is an item key composed of one or more selected photo images, 
together with notes concerning their interpretation, assembled by an individual interpreter, 
largely for personal use. 
(3) A photo index key is an item key composed of one or more selected photo images, 
together with notes concerning their interpretation, assembled for rapid reproduction and 
distribution to other photo interpreters. 
(4) An integrated-selective key is one in which-photo images and photo 
recognition features for any individual object or condition, within a subject or regional 
key, are so associated that by reference to the appropriate portion of the key the object 
or condition concerned can be identified. 
b. Elimination keys 
(1) A disc key is one in which selected photo recognition features are grouped 
or arranged on one or more discs so that when the recognition features are properly aligned, 
all but one object or condition of the group under consideration are eliminated from view. 
(2) A punch card key is one in which selected photo recognition features are 
arranged in groups on separate punch cards so that when properly selected cards are superimposed 
upon a coded base, all but one object or condition of the group under consideration are 
eliminated from view. 
(3) A dichotomous key is one in which the graphic or word description assumes 
the form of a series of pairs of contrasting characteristics which permit progressive elimination 
of all but one object or condition of the group under consideration.