How do you make blueprints?

[Grainfarmer]

For my windrower I took some good pics from the web. A good photo of the side wiew for example worked well to take some dimensions (length of the hood, wheelbase, cab, longitudinal beams of the chassis...), when I compared it with the dimensions of the brochure and the specs.
But: depending on the size and angle the photo was taken some dimensions may be skewed on the photo...
I let the best pics enlarge in a copyshop, that they were close to my scale 1/16. The differences that stayed I scaled down (example -10%). Comparing now the result I think that I proportioned it with a relative small deviation.
This may work fo a short model, but I have my doubts that you can do it this way for a 50 ft trailer...

[Straywolf]

Thank You everyone for the help i think i am gonna try that cad program.