Most digital cameras save pictures on memory cards. When you take a picture with a digital camera, the image registers on the camera's light-sensitive image sensors, but then the image has to be saved to memory. For this reason, memory cards have been dubbed “digital film” by digital photographers, since they now serve the same function as film. While the camera may come with basic storage, which is often called internal memory, you will usually have to add a memory card to save more than a few photographs.

Memory cards and the internal memory of the camera use a computer technology called Flash, or nonvolatile memory. This allows a digital device to save (“write”) information to memory, and that information remains in memory even when the device is turned off or is not powered. Because memory cards use electronic memory, they are very fast and reliable, as there are no moving parts such as a hard drive has.

Memory cards and the internal memory of the camera are different than RAM memory in a computer, for example, which is temporary — it vanishes when the power is turned off. Memory cards keep everything that has been stored. The cards can be removed, stored, and inserted in other devices with no loss of data.