Creating contour lines from our DEM GeoTiffs is covered in this conversation:
We generally quote our accuracy to be around 1%. Slightly better than that can be achieved with very high end cameras, lots of overlap and a relatively small area.
The best way to get accurate outputs is to collect lots of overlap, we a camera of good quality in good lighting conditions.
A lot of the jobs being posted using the DJI Inspire 1 and the Map Pilot app to collect the data are getting very good results on par with systems that cost 10x.