Resizing and Adding to an image

[rich2005]

Quote: I've resized an image to add some space to the bottom of it. When I do that what happens is that I get the added space as 'transparent.' i.e. it shows up as that checkerboard pattern which means that its transparent. If it helps, my foreground color is white.

First a probable cause. 
Using Image -> Canvas size (1) keeps the layer boundary. Use settings as (2) for a resize.

Of course there are other ways, pasting an image into a larger canvas for example so look for that dotted line indicating the layer boundary.

   

How to fix it. 
Usual way is Layer -> Layer to Image Size (3) then there are two cases.
The original image has no transparency and the expanded area fill with whatever background colour is set.
The image layer has transparency (4). Boundary changes, you can now use it. Want to fill with a colour? Various ways, example a new layer underneath or enable pixel lock and bucket fill.