How to Use Gimp to Make a WordPress Blog Header

1. Determine the size of the header image. This varies, and finding the answer will depend on which of the many WordPress themes you are using. If you are using Twenty Ten, the default theme that comes installed when you first use WordPress, the dimensions are 940 by 198 pixels.
2. Click on File and select 'New Image.' Set the width and height to match the dimensions you determined in the step above. Click on the 'Advanced' options and set the image resolution to 72 pixels per inch. Click on the 'OK' button to create the image.

3. Use the paint bucket tool to fill the image with a background color. Then add a layer and add some content. This can be a photo or part of a photo, or some text. If you put each element on its own layer, you can manipulate them separately.
4. Add a special effect using one of the filters in the Filters menu. You can add a drop shadow to make something stand out, for example.
5. Save the file as an XCF file, which is the native file format for the GIMP. This will preserve the layers and text modules so you can edit them again if you need to do so. Then use 'Save as' to save the file again as a JPG or PNG file so you can upload it as the header for your WordPress blog.