The following video posted on Youtube by someone called Ekeresco Jack dated 1 March 2017 I think is an excellent example on proving a flat earth. In this he compares six high-points of mountains located 77,4 km up to 120 km away. The tops also vary with height. Of this he made 2 reference models.
So from the top-point he extended the lines so from our line of sight projected 120 km away and compared them with what he actually sees on the photo. For the flat earth model these lines correspond with the photo, but for the globe model they don't match and there would be less to see also. This video is a must see for everyone who still has doubts regarding a globe or a flat earth. Edit 22-3-2017: This video disproves that the earth doesn't have a radius of 6371 km, but shows that it is much more flat. It suggests a flat earth, but there might also be some kind of curvature.
The tops of 6 mountains are projected from our line of sight for 120 km away. Doing this one on one results in the flat earth model. For the globe model he needs to deduct the height of the curvature also. When doing some of the lines change position and some actually swap places in reference to the flat earth model. Both models he projected on the photo.
Check on used heights
Using the site of koordinates.com I did check if in this area the heights are corresponding with what is shown in the video. As you can see in the results that the maximum in this area is 2300 m (at about 124 km from Wellington), which corresponds with the 2360 m at 120 km. This also confirms that the used data in the video is reliable.