Original map screenshot Easter egg
From Halopedia, the Halo wiki
The original map screenshot Easter egg is an easter egg in each of the multiplayer maps released in the Halo: Reach Anniversary Map Pack. Each multiplayer map has included a screenshot of the original map it is based on. It is recommended to find them in Forge.
On High Noon, the screenshot of Hang 'em High can be found on the Blue Base side of the map, under the area labelled "Blue Bunker", right beside the hologram, and is part of the bridge in the area labelled "Lower Catwalk".