Copy & save text off an image to use again

[rich2005]

The best way is find the font used and replace that way. Next is careful tracing with the path tool but that takes a bit of practice.

There is rarely a general solution and there will be a few ways to accomplish.
Every image should be considered on its own merits.

For that particular image and assuming you want the text in the same place. Too many screenshots so not in-line

1. Isolate the text with a selection. You image is a tiny bit off horizontal so I used free select.
http://i.imgur.com/TFbu5Y0.jpg

2. Invert the selection Select -> Invert and fill with white. Kill the selection Select -> None
http://i.imgur.com/AicHCp0.jpg

3. For this image use Colors -> Components -> Channel mixer. Pull red to -200, green & blue +200, tick monochrome.
http://i.imgur.com/gCZBIOm.jpg

4. That gets black text on a white background, remove the white with Colors -> color-to-alpha (white is default)
http://i.imgur.com/ZzrBFPf.jpg

5. Lock the transparency with the alpha lock, top of the layers dialogue, bucket fill with whatever colour you want.
http://i.imgur.com/alc9Sq9.jpg

remember to turn the alpha lock off, when complete.