IEVision includes many OpenCV features, but not all of them. More likely you can do this using standard ImageEn. What method are you looking to use insert the invisible watermark. Generally it is done by overlaying an almost completely transparent watermark image.
Yes, there are a number of discussions on the web of the best way to do this. Generally, you would avoid easily circumventable options like meta-data. If you overlay an almost transparent image over the image then that is invisible to the naked eye, but can be detected by comparing the watermarked image with the source.
procedure TMainForm.test1Click(Sender: TObject);
// Stretch result so easier to see
diffs.ImageEnView1.Proc.AutoImageEnhance3( 1.0 );
Here are the two source images (second one has white text drawn at 2% opacity by merging a text layer):
Here is the difference view:
Of course, being a JPEG there are encoding artifacts. If you use PNG the difference is much more crisp:
This is just a simple example. You could code a better solution by iterating through the scanlines and doing a more targeted comparison.