X11 APIs have no security and they don't work in Wayland. Either one of those reasons is enough to avoid using them.

Aside from that, it's the slowest and worst possible option in X11 because it copies the pixels into the socket. To handle large images you want to at least use MIT-SHM. XGetImage should only be used as a fallback. Or better, just don't use X11 APIs at all.