You can stitch an outdoor scene with a shuttlecraft like that together better by making it 400% final size then adding slight blur and downsizing to 25% with any image-editing software. I've done that with photos and gotten the same results you'd expect with Photoshop. It works because at a larger size the jagged edges are relatively less jagged unless you've simply blown up a smaller original after cutting out something to paste in. So the color blending done with size reduction takes its information from a higher-res image and yields nice results. So if you're cutting an image to paste into a scene, start at 400% final size or larger so that your cutting will be at sufficiently high resolution before bringing down to final size.