People sometimes ask how many digital photos can be stored on a CD or DVD. That fact of the matter is that it is very difficult to say with precision the number of images.
Image file sizes vary according to the type (JPEG, RAW, TIFF, Video), resolution and the compression level you set in your digital camera. The size of a digital image, even shot at the same resolution, can vary due to the colors in a scene.
Brightness of colors influence file size
The number and degree of the brightness of colors in a scene can influence file size. Additionally, if you shoot a subject in black and white, the file size will be a smaller than if it been had shot in full color.
Editing, such as cropping and decreasing the size of an image, can also significantly decrease the size compared to the original file. When you edit, however, always work on a copy of an original but never the original itself.
The average size of a five megapixel color image file is between 2-2 1/2 megabytes when shot at JPEG fine (least compression). That means you can get about 280-300 onto a CD that has a 700 megabyte capacity.
The most important thing is not how many digital images can be stored on a CD or DVD, but that you back up originals of your photos.
An alternative: storing image files online
Increasing numbers of photographers store digital photos with online photo hosting or storage services. Some of these services offer one to five gigabytes of free space. Additional storage can be purchased for a modest annual fee.
Online services, such as Mozy, offer unlimited, automatic online backup for all types of files, including digital images and video. Many consider these types of services more reliable than other archiving and storing methods.