Please provide answers with either reasons not to have such a tag or with one tag recommendation.
In my opinion such tag for only a purpose of image related measurements would be an overreaction. But, since we approved an existance of secondary tags I think
A good wiki description is required to avoid overdosing it with/instead of list-manipulation.
One tag that would fit is mensuration. My thought was to just add it and write a brief-form tag wiki for it (see below). But, deferring to Mr.Wizard's question, I offer it here first for approval.
Questions related to the measurement of geometric magnitudes of 2D and 3D objects represented as Mathematica objects or depicted as areas or voxel-regions in an image.
I propose to use computational-geometry.
It has a very short, uninformative wiki at the moment, but in my understanding, this covers measurements and similar as well. From Wikipedia:
"Computational geometry is a branch of computer science devoted to the study of algorithms which can be stated in terms of geometry." 1
Furthermore, geometry (especially Euclidean, and that is what we use here most of the time) has strong links to:
"computational geometry, computer graphics, convex geometry, discrete geometry, and some areas of combinatorics." 2
Also, geometry of a space involves calculations of topology and metrics defined over the space, which (I would say) is exactly what the example question is about (identify, count and measure geometrical properties of particles).
As an independent act, the tag wiki should certainly be improved.