In this GIMP tutorial I show you the basics of how to remove an object from an image and replace it with a background. An overview of the steps:
1. Copy-paste a bunch of new layers from the background using the Free Select tool
2. Add layer masks to get rid of hard edges
3. Combine all the layers with Layer from Visible
4. Use the Smudge tool to blur any remaining hard edges
Tip: Use the Layer Transform Flip Horizontal effect to make things like background trees seem different. You can tell a bad photoshop by repetition, so try to get rid of repetitive elements!