How to get an idea about the resolution of a captured photo?

Resolution usually means the number of pixels per inch (or centimetre) which a monitor or a printing device is capable of displaying/printing. Sometimes (for monitors) it is quoted as the total width x height (in pixels) of the screen. The word 'Resolution' when applied to photographs is the number of pixels per inch in the printed result (or as displayed on the monitor). A pixel is the smallest element from which all digital images are made. It is a tiny block of a single colour from one of (usually) 65536 colours available. This is called a '24 bit' image because each pixel takes 24 bits - 3 bytes - to store. The pixel size of an image is therefore related to the file size because an image which is 2592 pixels wide by 1944 pixels high will consist of 5,038,848 pixels (about 5 million) and will therefore be called a '5 Megapixel image'. Since each pixel takes 3 bytes to store, the NOMINAL file size will be 15,116,544 bytes (or rather more than 14 Megabytes). Because nearly all camera pictures are compressed using a standard set by the Joint Photographic Experts Group (JPEG), the ACTUAL file size on disk of a photograph is considerably smaller. If you were to print your photograph on a printer at 360 dots per inch, the size would be approximately 7" x 5". If you wanted your photo printed so that the size was 14" x 10", then you would need to print it at a resolution of 180 dpi (and, at that resolution, you would just begin to be able to see the individual squares of colour that the photo was made up of and you would say that it looked slightly 'blocky' or 'not very sharp'). Monitors, however, work at a MUCH lower resolution of somewhere between 75 and 96 dots per inch, so your photo (on a 75dpi monitor) would measure about 34" wide (too wide for most monitors). The reason that such a large image doesn't look 'blocky' (and also looks a lot more 'alive' that when it is printed) on a monitor has to do the the shape of the individual dots and the fact that the monitor is emitting light rather than absorbing it. To sum up, therefore resolution means the number of dots per inch at which a picture is displayed or printed and so it directly affects the displayed size of the image. You can talk about the resolution of a monitor or a printer and you can talk about the resolution at which a particular picture is printed or displayed but you cannot talk about the resolution of a photograph UNLESS you mean the [u]size of a photographed object (at a specific distance from the camera) which can be displayed as exactly one pixel[/i]. I hope that that makes it clearer for you!