Can copyright metadata in a TIFF be locked so others can’t remove it?

No. In practice, metadata in a TIFF cannot be reliably locked against removal or editing. Anyone with image-editing software can usually open the file and resave it without the metadata.

If your goal is attribution protection rather than just metadata entry, the usual alternative is watermarking. A visible watermark is harder to ignore, while a digital watermarking system such as Digimarc may help embed identifying information more robustly. However, these approaches still don’t make the file impossible to alter.

Steganography was also suggested in the community replies, but it is not a standard or dependable replacement for copyright metadata when distributing images, since reprocessing or resaving can break embedded hidden data.

So the practical answer is: add copyright metadata for honest users and workflow compatibility, but don’t rely on it as something that can be locked or made tamper-proof.