Understanding picture resolution
Resolution, and in particular, photo resolution, is a feature that confuses many. This shouldn't be an issue because the resolution of a camera is a fixed quantity and only changes when you physically choose a different picture size in the camera menu—or if you crop the file on a computer.
To be pedantic, resolution is not only about the number of pixels in the camera, although this is important. Resolution is also influenced by the quality of the glass elements in the lens, the camera's image stabilization technology (indirectly), and the shooting technique employed by the photographer.
The biggest point of confusion arises from the way the number of pixels per inch (ppi) can vary widely from camera to camera. In the printing world, dots per inch (dpi) is the same as ppi, which in turn is the same as lines per inch.
Different resolutions = different viewing sizes: Demonstrating resolution can be daunting...