To make a copy of a key you need a detailed photo and one measurement to scale the dimensions.

When taking a photo its best to take it from some distance and then crop it to avoid lens distortion, which will mess with the dimensions.

For the scale, measure long features (eg. lenght of the key) to minimize measurement error.

Next add your photo as a canvas in Fusion 360, then scale the model entering the previously measured value. After that create a skech and outline the shape of the key and extrude it.

Print instructions:

• Print with maximum wall thickness
• Layers should be parallel to key length to achieve strong print
• Use material that isn't brittle

Thanks to this method I was able to reproduce a working copy of lost key to my ebike battery (stl + step avilabile to download)