userid for posts/attachments

[mangus580]

Ok, I am trying to take a watermark modification that creates a watermark on the hook of attachment_display. The mod works fine the way it is, but I would like to add the posting username to the watermark on the fly. On our previous forum, I was able to write the code so it did it upon upload. Due to technical (security) reasons it messes up the image doing it this way... so I figured doing it upon view will work.

Here is my issue. I need the way to pull the userid variable for the post... so that I can create the watermark for that user. I have tried everything I can think of, and nothing yet has worked.

What would the variable be for this???