1. Open image in SnagIt
2. Colors > Color Substitution...
3. Use the dropper next to "Old color:" to select watermark color
4. Click box next to "New color:" to select replacement color (generally this would be the background color)
5. Goodbye watermark!

UPDATE: CyberDoc and Mike Mills kindly recommended the freeware PhotoFiltre (installer-free version available), which worked every bit as well as SnagIt. It's as simple as clicking Adjust > Replace color and using the droppers to select. Initially, most menu items were grayed out for the GIF I had opened, but Mike informed me of the solution: Image > Mode > RGB color. Thanks to you both!

/windows | Apr 12, 2009