To center an image in GIMP you need to do two things:
- Create a vertical and horizontal guide
Click image -> Guides -> New Guide (by Percent) -> Select horizontal -> 50%
Repeat the process for a the vertical guide
- Ensure “Snap to Guides” is ticked
Click view -> Tick "Snap to guides"
You can now insert a new image and drag it close to the center and it will “magically” snap to the center of the canvas.
Sometimes it’s nice to force people to read instead of watching a video 🙂 Nonetheless, here is a screencast of how to center an image in Gimp.