looking for free software to interactively extract models from images with

[Dan Hitt <dan.hitt@gmail.com>]

Hi All,

I'm looking for a piece of free software that can display images
(such as jpg) and interactively extract data (or form models)
from them.

So this would be something like the measure tool in gimp,
but much more involved: instead of having a single line segment
which you compare with the horizontal (as in the gimp),
you could form and save complexes of points and lines.

Saved along with these complexes would be their
associated lengths and angles, and you could then use them
on other images (such as by identifying
corresponding points on two different photographs).  Perhaps
other options would include some kind of transform, so that
you might select the vertices of a quadrilateral and transform
the images so that your four-sided figure becomes a rectangle.

So i'd be grateful for any suggestions on what piece of free
software comes closest to being able to do this.

Or, if this is the wrong group, please steer me (but i'm
asking here because the people who post here have such
a breadth of knowledge about so many topics).

(I think i'd prefer something compiled over something interpreted,
and probably something written in python over something
written in java, but beggars cannot be choosers, so interested
in any leads whatsoever.)

Thanks in advance!

dan