Though information varies on the exact amount, the SD Association rates a 2 gigabyte SD card at approximately 700 images from a 10 megapixel camera. Storage amounts vary based on the number of megapixels in an image, the file type of the image and the compression used for the image.
As the megapixels increase, so does the storage size of an image. Some cameras don't compress image files as heavily as others, affecting storage space. Most cameras save images as JPEGs, but older models may use BMP files, which increases the storage space needed. Since most digital cameras shoot video as well, the storage capacity for images is decreased when video files are present.