actually, there is something called, "meta data." here is a few words on the subject.
Metadata in JPEG Files
The JPEG file format is the format most used for storing and transmitting photographs on the Internet. In addition, a large number of digital cameras store pictures as JPEG files. However, many users are likely to be unfamiliar with the fact that a JPEG file can contain other data besides the actual photograph.
The JPEG file format allows it to embed additional information called "metadata" in the file header. (Other image file formats can contain metadata, too.) The purpose of these metadata is to provide additional and useful information along with the picture. Image manipulation programs and especially digital cameras take advantage of this feature.
Metadata can be embedded in different ways. A common way is to store them according to the Exif specification, which has been created by the Japan Electronic Industry Development Association (JEIDA). Other popular specifications are the IPTC headers defined by the International Press Telecommunications Council (IPTC) and XMP developed by Adobe Systems. More detailed information about these metadata formats as well as descriptions of other metadata formats can be found on ExifTool's Tag Names page.
Among other things, the metadata section of a file can contain information about:
* make and model of the digital camera
* time and date the picture was taken
* distance the camera was focused at
* location information (GPS) where the picture was taken
* small preview image (thumbnail) of the picture
* firmware version, serial numbers, name and version of the image manipulation program, etc. ...