If you look at almost any of my recent uploads the watermark includes an image as well as my name. This is how I add them.
You'll have to experiment with size - I upload my photos at about 840 pixels wide, and for that I create my watermark in a 400 pixels wide by 100 high file. Create your new image file, making sure that the background is set to transparency. I add my images using brushes:
The brush tool is the 6th one down on the right in the Tool Box, it looks like a paint brush.
When you click on it the Paintbrush dialogue opens up at the bottom of the tool box.
The default brush is a circle, but if you click on that it will open out a box which shows all the brushes you have loaded.
The default ones in GIMP are pretty limited - there are round brushes, feathered brushes, a green pepper and few other odd things.
So long as you're using version 2.6, then any paintbrushes for PhotoShop (.abr extension) should work, but there are also plenty of free GIMP ones available for download.
DeviantArt is one place, but if you Google GIMP paintbrushes or PhotoShop paintbrushes you'll find all sorts of styles.
Download the ones you want, making sure you know where they are downloading to.
Mostly they come as ZIP files, so then you need to unzip them.
This is the best way I have found of adding downloaded brushes into the GIMP library. I know it's complicated, sorry about that.
Open the C drive.
Open Programs.
Open GIMP folder.
Open Share
Open Gimp
Open 2.0
Open Brushes.
Now copy and paste, or drag and drop, your downloaded brushes into that folder.
If you had GIMP open, close it and open it again, and when you click on that brush option in the Brush dialogue, you should see all your lovely new brushes.
They really work like a stamp. Choose the one you want, and you should see a dotted outline when you hold it over the file you're pasting it into.
If it's too big, then go back to the brush dialogue box and change the scale down a bit.
Once it's the size you want, just place the cursor where you want it to be in your text box and click once.
Don't hold your mouse down or you'll get an effect like painting with a shaped brush.
You can change the colour where you change text colour, if you want it more or less opaque there's a box for adjusting opacity in the brush dialogue.
Add your text box and text the normal way. I usually use two text boxes as I make the month and year a smaller font size.
Make sure to save as a .png, and NOT as a jpeg, as you need the transparency to be maintained.
Any questions, please feel free to send a pm
.