[Greg McKaskle]

The size estimate is not too bad even if you ignore the distortion. A better approach, though a bit more expensive would be to use the bounding box to inspect the original image with edge detection methods. You could probably go so far as to find all four corners. But again, once you have a good pixel size for something in the image that you know the physical size, you are able to solve for distance.

As for using the tape width, that is the smallest known element in the image. That will degrade with distance faster than using a larger known size. But as mentioned, it will work provided you are pretty close.

Finally, you can estimate distance several different ways and compare them for accuracy, perhaps even using averages or other techniques for producing a better value than a single technique.

Greg McKaskle