At the highest resolution, more details become clear, and the image is sharper. In the last picture you can see additional details around the eye that are fuzzy in the previous picture. The spatial resolution of images acquired by a sensor system is normally expressed in cycles or line pairs per millimeter. It can also be expressed in terms of the smallest object that can be identified at a fixed distance. The same is true of ground based imaging systems.
Resolution defines the distance at which objects can be seen and identified.
In the picture above, a person experienced in viewing different birds may be able to identify the Toucan from the second picture, but most people would need the resolution of the third picture.