Playing with G'MIC, I came across a most awesome filter! When it works, it's incredible! Sadly, on my machine, it crashes/malfunctions more than it succeeds. It's the Fourier Watermark filter. I am ecstatic when it works, and I am hoping a developer sees this. I will try to contact them with my concern.
This first image, is the result of running the filter on a smaller sized version of my original image. A larger file size crashes the plugin. If the entered text is too long, the red, green and/or blue channels disappear! Here I reduced it enough and shortened my text enough to do this demo.

Go to Filters>G'MIC>Spectral Handling>Fourier watermark and put in your secret text. This was my result. Looks exactly like the original.

After saving the image, I opened it in Gimp and ran the "Fourier Analsis" filter in G"MIC and got this next image. Like I said, I love the filter. They need to fix memory holes to get it right! I soooo need this filter!!

I just tried that on a small image. That is way, way cool. How large was the one that crashed on you?

Nice way to watermark your work. =)

It's a 3mp image (2048x1536). Short of reducing the image size and putting a very little bit of text, I can't get it to work without crashing. I was hoping to keep my existing image size, and putting in an actual copyright message.

I am taking my full sized image, selecting a center rectangle, copying it and creating a new image from the copy. I run it on the copy and paste it back into the original. By doing it from the center, it lines up perfectly and when I merge it down it fits perfectly. I need to reselect and copy the center, and then make a new image from it, in order to view the hidden text. Still looking for a better way.

Have I said how much I love Gimp and G'MIC? I posted on the G'MIC forum on Flickr, about this issue and within 24 hours the author of G'MIC had updated the codes in G'MIC. All I had to do, was to hit the refresh button in G'Mic and it grabbed the update, in less than 1 second. It now works perfectly on a 12mp (4288x2848)file! This is beyond impressive!! Here is a little demo box I threw together! It shows a part of the image before the watermark, the same area after adding the watermark, and the same area after G'MIC revealed the hidden watermark. I Love It!!!