This function is currently not documented; only the argument list is available.
This function is EXPERIMENTAL. The behaviour of this function, the name of this function, and anything else documented about this function may change without notice in a future release of PHP. Use this function at your own risk.
Hides a digital watermark within the image. Recover the hidden watermark later to prove that the authenticity of an image. Offset defines the start position within the image to hide the watermark.