There is open source software that does this. ImageJ is a free open source java software that does just this. It is well known among scientists and was developed by the NIH. Best of all, you get to choose your own calibration device. I've used it to measure biological specimens of sizes 1-3mm in size from a high resolution photograph taken with a Nikon D100 together with a 1/2 inch calibration block. I've been happy with the results. Besides measurements, it does a whole bunch of functions like counting particles and image processing
Since it is java based, there are versions of Windows, OSX and Linux. Of course it does not address perspective problems, but that is not an issue for me as I can keep my calibration device in the same plane as the item I am measuring.
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There is open source software that does this. ImageJ is a free open source java software that does just this. It is well known among scientists and was developed by the NIH. Best of all, you get to choose your own calibration device. I've used it to measure biological specimens of sizes 1-3mm in size from a high resolution photograph taken with a Nikon D100 together with a 1/2 inch calibration block. I've been happy with the results. Besides measurements, it does a whole bunch of functions like counting particles and image processing
Since it is java based, there are versions of Windows, OSX and Linux. Of course it does not address perspective problems, but that is not an issue for me as I can keep my calibration device in the same plane as the item I am measuring.