What are the rules for making reference images

What are the rules one has to follow when formating images for use as references in blender. Stuff like ratios, proportins etc.

If you UV-map the blueprints on to planes, you won’t have problems regarding image size as long as the references are in same ratio.

Another option would be to use Rotobox script. It basically does the same thing but afaik you have to be more careful with image sizes.

How to UV-map blueprints on to planes: https://blenderartists.org/forum/viewtopic.php?t=55526&highlight=

I have a nice system that works for me:

I create a 1024x1024 image, and sketch the front. I center the image, and if I’m going for complete symmetry I copy and paste the better half over the bits I don’t like.

Since Blender doesn’t have images that are mapped to views (you can set up an image to map it to viewports, but if you change from front view to side view in that viewport it doesn’t change the reference), I place both reference sketches on the same image. Then I move the model in 3D space so that in the front view it sits in front of the front image, and in the side view it sits in front of the side image.

I’m posting an image I drew, in the off chance it might help you. It was two 1024x1024 images that I just pasted together. Note that a lot of the points on both images don’t exactly match up; I’m not the best hand artist, so I do a rough sketch and then fill in the blanks with my modeling.