As of this writing, the most reliable source for legacy DS-2CD1021-I firmware is the Hikvision Europe Download Portal under "G0 series IPC." Always checksum-verify the file if possible.
: New firmware can stabilize older hardware, improve image quality, and fix known bugs. ds-2cd1021-i firmware download
: Log in to your camera's web interface. Go to Configuration > System > System Settings > Basic Information to check the current Firmware Version Property (e.g., "G3" or "E3"). As of this writing, the most reliable source