As a rule in photography you can't add detail to a photograph which isn't there in the original. Photos which have been taken at a low resolution can be upsized but the detail in the photo will remain the same. As a rule it is always best to have your camera set at the highest quality available. If space is an issue you can buy a bigger memory card. Remember a photo may look ok on your computer display but it may not necessarly be of high enough quality for printing.
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