Found this interesting site for measuring dimensions from photos / images. The first dimension you measure is your 1.0 scale. I used the width of the body tube since that was going to scale this to a BT-80 main tube. If you know the length or other dimension of your scale rocket / missile you could use this. You can export your dimensions as a table from the site and can save the image with your annotations.
https://eleif.net/photo_measure.html
https://eleif.net/photo_measure.html