The GIF and PNG formats support making any selected area transparent. The tricky part of this is to select the area to get all and only the pixels you want to zero out.
I recommend using the Select by Color tool from the Tools Palette and select one of the goldish pixels. Use Shift+click to include more shades of gold until you get them all, and then clear the selection (Edit>clear). Here is a rather large (6 Meg) video tutorial on this in Ogg Theoria format.
Useful tip: You can always shut off the "active selection" boundary (the "marching ants") with Ctrl+A.
2. selection tools
The uniform background is just a simple case of selection; anything that can be selected can be made transparent (as well as modified in a great many other ways). You can also select by geometric shape (rectangle, ellipse), freehand line drawing, magic wand, or Bezier curve drawing tool. Using the selection tools takes experimentation and practice. ↑
3. sharpening and correcting for color cast
Many images imported via a scanner or from a Kodak Picture/Photo Cd need color adjustment and sharpening. These (and most) filters work only at full color ("RGB") depth, so the first thing to do if your image is not a jpeg or other 24/32 bit color format is to choose "Image" (under right mouse button) and select "RGB" if it is not already selected (unless you want Grayscale). (This is also where you can "Scale" (ie. resize) your image.)
To sharpen a blurry image, you can use either "Sharpen" or "Unsharp Mask"; the latter is usually better because it does not sharpen dust spots. Note: Some sharpening is nearly always needed after you resize an image (down).
To adjust color levels, Tools>Color Tools>Levels. Try "auto" to equalize the color balance. You may want to increase the Saturation with "Hue-Saturation" also.
Correcting color casts is often successful with Colors>Auto>White Balance; can add Colors>Auto>Color Enhance ↑
4. Using T(ext)
"T" in the Toolbar is for inserting text in an image, and you can select DynText by double-clicking on the T. To use regular Text,
.html extension and then paste it into the main document containing the image. [Note that this file includes the image.]
Hang onto this file, because if you want to add to or change the imagemap, you need to load it back into the GIMP Imagemap editor. (That is, the Imagemap editor can't read and write to an entire HTML file.) The Grokking section is good and not much out of date, but does not warn you about saving the map file. To reload the saved file and edit the imagemap: first load the image into GIMP, then call up the Imagemap editor. Then Open the map file, which should cause the current links to appear in the right window. Edit and save, then re-insert into the larger HTML file. ↑
6. Drop Shadows
The Drop-Shadow plugin (Rt-click on canvas; Script-Fu>Shadow>Drop-Shadow) gives many options for density, sharpness, and location of the shadow. The plugin adds the shadow to the selected area, so if you want to add shadow to Text (and not to the whole box), make sure the text is selected when you add the shadow. Drop shadows of more complicated shapes are possible also, in advanced GUG tutorials. ↑