Two question about watermarking

[life24]

Hello,
--Why is the watermark embedded into image instead of just inserting it into the file header?
2- What is the drawback of inserting additional information into images?(in watermarking)
Thanks

[snibgo]

I don't see how a watermark can be inserted into a file header. Most file formats don't a have a field for watermarks.

A watermark changes pixel values, so it makes processing the image more difficult.