This is one of those problems that sounds easy, but in reality is very difficult to do.
The photo angle, stitching process, etc. can all have an effect on the dimensions in the photos.
Take for example a sign at a junction; let’s imagine you are at a 45 degree angle to it. How do you measure its size? The answer is trigonometry – you need to know the angle to the sign, the distance from photo (and hope that the stitching is uniform).
Now for one photo you can just about do this manually, adding more photos changes the variables (angles, etc.) so you need to start from scratch.
This would be incredibly useful to do (I’ve wanted to measure the height of trees in our images). Alas, I have found no out-of-the-box solution or raw code that can do this. If anyone is working on this problem, I’d love to hear from you