The storage capacity of each device depends on

The resolution or image file format used to capture images.

The amount of compression used.

The number of images you can store is important because once you reach the limit you have to move them to a computers. or erase some images to make room for new ones.

There are two types used mainly Compact Flash (CF) and Secure Digital (SD). These cards store your image files on flash chips that are similar to the RAM chips used inside your computer but there is one important difference. Your photographs are retained indefinitely without any power to the card.

These chips are packaged inside a case equipped with electrical connectors and it's this sealed unit that is called a card. Flash memory cards consume little power, take up little space.

CompactFlash (CF) cards are about the size of a matchbook.
Secure Digital (SD) cards are smaller than CompactFlash cards and are used in over half of current camera models. MultiMedia (MMC) cards are even smaller cards used in a few pocket cameras.
One thing to consider is the "speed" of a card. Unless you are missing shots because your camera can't move images from the buffer fast enough, the bottleneck may be in your camera, not the card. When you first buy a memory you should format it. Formatting prepares a card for use in a camera, Be aware that the Formatting erases all of the images stored on a card. There is digital image recovery software available.

Some cameras come with software that lets you connect the camera to the computer and operate it from the computer so that captured images can be stored on the computer's hard drive in studio settings, or in landscape photography to immediately check photos on a larger screen.