Camera lenses sometimes show an image error, which becomes more and more prominent at higher resolutions: chromatic aberration. It concerns a slightly different image scale for the individual light wavelengths (colors). For example, if a picture shows a car, the red illustration is a little smaller than the green and the blue one.
The result is that the picture looks normal in the center, but the high contrast edges in the corners have a colored fringe. This phenomenon becomes easier to see with more pixels. However, if the camera has a good internal image processing, it is possible for it to compensate. The picture editing software commonly-used does not have the appropriate tools for correcting chromatic aberration.
For a more extensive description, see the knowledge article "Chromatic aberration".