It uses the zig build system to download and compile OpenCV, OpenCV contrib, and GoCV (which is used for its C bindings to OpenCV).
It also uses the same nominated version as zig-gamedev (and Mach I think) (update 2025-03-02: it’s slightly behind theirs now)
Code here: glitchcake/zigcv: Zig bindings for OpenCV 4 - Codeberg.org