UPDATE/EDIT: The "socker pitch for scale" might be the 2 pixel wide small dot, almost indistinguishable from the beginning of the curved arrow pointing towards the blown-up version of the soccker pitch. One can hardly see it in the zoomed version of the image, with a little bit of imagination.
(ILC overall length: 31km, 724 pixel. Socker pitch: 80 pixel, 31km / 724px * 80px = 3.42 km; a vector drawing corresponding to the screenshot can be found in the technical design report, Volume 1, §3.1.1, fig. 3.1)