Resolution is determined by pixel dimensions or the number of pixels along the width and height of an image. The display size of an image on-screen is determined by the pixel dimensions of the image plus the size and setting of the monitor. The file size of an image is proportional to its pixel dimensions. Because your image may be viewed on a 13-inch monitor, you ll probably want to limit the size of your image to a maximum of 640 pixels by 480 pixels. An image with a high resolution has more pixels and therefore a larger file size than an image of the same dimensions with a low resolution.
Picture quality is dependant upon the original picture quality or the scanned quality.
Increasing the resolution of an image scanned or created at a lower resolution only spreads the original pixel information across a greater number of pixels and rarely improves image quality. Monitor resolution depends on the size of the monitor plus its pixel setting. The typical resolution of a PC monitor is about 96 dpi, of a Mac OS monitor 72 dpi. In Adobe Photoshop, image pixels are translated directly into monitor pixels. Thus, if the image resolution is higher than the monitor resolution, the image appears larger on screen than its specified print dimensions.