Today’s digital cameras produce large images, on average 5-6 megapixels or 2-3 megabytes (MB) in size. These images are too big for sending by email or for publishing on web. If you are sending photos for example of your family to your relatives you should shrink those images to 1 megapixel or less (size up to 1024×768 pixels and file size around 100 KB). That is the appropriate size for email. You would not want to receive 10-20 MB of large photos in your mailbox, especially if you are not on broadband.
There is a simple free utility from Microsoft that will help you shrink digital photos with few mouse clicks.