Have you been wondering how I know what camera you use, or what settings the pictures were taken with? All of this information is stored in your picture, in a format known as Exif data. All you have to do is have a program that can view it. There are many programs that will let you view the Exif data from a photo, but to do that, you must have the photo already on your hard-drive. I don’t want to have to download every picture from this forum just so I can see the Exif data, so I use a plugin for my browser. This plugin for Firefox allows you to view the Exif data straight from your browser, eliminating the need for downloading it, then viewing it from your hard-drive. Once you install it, you just have to right click the on the picture and select “View Image Exif Data” from the list of options.
There is an excellent article at photographylife.com on the subject.