For each image in {HEAD ~ a database} of {TAIL ~ images} having known regions of interest, global image features are measured and an image characteristic index is established based on these global image features 
of
For each image in { HEAD ~ a database } of { TAIL ~ images } having known regions of interest , global image features are measured and an image characteristic index is established based on these global image features
OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH