Instant Alpha

I'm trying to make the background of an image go away so that I just have the object in the image and the background transparent. Now, I tried in instant alpha in preview and this is what happens:

I get these dotted lines around the giraffe. I then press enter and instead of showing me the giraffe with a transparent background, I see this:

I don't know what to do with this. Is this my transparent image? I know how to do Instant Alpha in Pages, but I do not know how to get the transparent image from the pages document to my desktop. I would also really like to know how to do Instant Alpha in Preview. Does anyone know what I should do after this to retreive my new transparent backround image?

Thanks So Much