Hello larrywag,
You can permanently watermark your photos by doing the following, make sure you are only watermarking duplicates so you do not destroy the original file.
1. Locate a picture on your Mac using the Finder. Right-click the file you would like to watermark or “Control” and click it if you do not have right-click enabled. Select “Duplicate” to create a copy of the original image. Double-click the copy to open it in Preview. If you have set another program to open image files, select “Open With” from the File menu and select “Preview.”
2. Click the “Tools” menu, select “Annotate” and then click “Text.” The cursor changes to a cross symbol. You will now drag the cursor over the image where you want the watermark to appear. A rectangular text box appears on the screen.
3. Type the text you want to use as a watermark, like “yournamehere” or your company name. Press “Command-A” to highlight the text you just typed.
4. Click the “Font” button that appears above the photo, which looks like the letter “A” The font window opens. Change the font and font size as desired. Click the “Text Color” button at the top of the Fonts window, which is a colored square located beside the letter “T.” The Colors window opens.
5. Select a color in the Colors window. In most cases, watermarks look best when they are white, but you can choose any color you like.
6. Locate the Opacity slider near the bottom of the Colors window. Drag the slider towards the left until the number beside the slider is at 10 percent.
7. Click anywhere on the image to deselect the highlighted text so you see how the watermark will appear once the file is saved. If the text looks too faint or if it’s not faint enough, highlight the text and change the opacity level as needed.
8. Now click the “File” menu and click “Save.” Now the watermark is embedded in the duplicate image so you wont run the original file.