DPI is an acronym for 'dots per inch.' It is a measure of how much information, pixels in the case of digital images, is contained in one inch of space.

Changing the dpi of an image will not add any detail to the image. Changing the dpi will only change the physical size of the image. For example, if you record an image with the PowerShot S40 camera at the largest resolution setting, the camera will create an image that is 2272 X 1704 pixels in size. At 72 dpi, the image will be 31.5 inches wide. You can calculate this size by dividing 2272 dots by 72 dots per inch. At 180 dpi, the image is 12.6 inches wide. Since the image is larger at 72 dpi but you do not have any additional information compared to the 180 dpi image, the larger image will appear to have less quality.

If you choose a higher dpi in an image editing program without changing the number of pixels in the image, the image will shrink in size. If you leave the size the same and increase the dpi, the software will need to add pixels to the image to fill in the missing data. Based on how well the computer can "guess" at the added pixels, the image may not look better at the higher dpi.