Extreme barrel distortion. It's a fisheye shot made at full telephoto zoom. At this scale it's hard to see the bit of chromatic aberration here. Look hard at the contrast edge of the right tree. If you just shot a picture that needs its barrel distortion fixed, you are in luck.
Barrel distortion creates images that look like they ate too much.
Straight lines near the borders tend to curve outward. It's extremely difficult to fix in film and a snap to fix on your computer. Thanks to iNovaFX, special filters do this that are a match to your Nikon zoom and wide angle lenses. Now panoramic segments can be shot with the wide angle converters and, after being zapped by the iNovaFX filter, straight lines at the edge are pixel-perfect straight. Stitching images can now proceed as if nothing had ever been amiss.