Most image files and digital photographs contain EXIF data. These are information embedded onto image files. It's actually a stardard for storing information onto image files. EXIF data can contain anything ranging from the file creation date to any information added by users or software. It even contains information about the camera setting if it is a photograph taken from a digital camera.
Phil Harvey created a PERL library for reading and writing the EXIF data. It allows you to use any scripting language to access the EXIF data. I've developed a form that uses his EXIF Tool. You can use it to read the EXIF data on any image file. Just type in the URL of any image or upload the image file and it will display the EXIF data.