Sorry Will, what you're trying to do with Paint in images won't work because the weather software can only process text files to replace tags .. the text inside of images is just light/dark pixels and can't be recognized as text to replace.
Some weather software does have the ability to generate graphics files with weather tags (like Weather-Display and WeatherCat), but most folks use something like Anole's PHP script (which you are already using for your banner) to create a image with weather values in it.
Best regards,
Ken