measure positions

[mrsiro]

Hello,
first: english is not my native language, so I try to keep my posts short and precise. What may not allways succeed
Ok,
Iwould like to measure positions with IM.
Background: I must verify the positions of several textblocks printed on documents.
The images of the documents will come by scanner or (better)camera.
So it would be helpfull to find f.e. left and upper borders of such blocks. If possible metric.
The blocks must be printed within a tolerance of about 1mm up/down - /left/right and there should be a warning when the block is outside of this tolerance.
So I only need to find the positions, everything else I may realize with PERL.

Many thanks in advance for any help

[snibgo]

ImageMagick works with pixels, not millimetres, but converting between them is trivial.

What is the visual difference between "text blocks" and the rest of the document? IM needs to be told what to measure, that identifies where text blocks occur.

Perhaps you can link to sample documents.