Question: How to get camera serial number from EXIF ?

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Edit: some folk think that not all (or even many) cameras store serial number, but I tried four from different manufacturers and they do. So, let's just rephrase it as "How to get camera serial number from EXIF if there is any?"

Answer: 
First the camera would have to write its serial number to the EXIF data. I don't know of any that do.

But in any event, you'll have to check with the documentation of the specific camera in question to see if it writes this value and where it writes it. There's no standard place for it, since it's not a standard thing to write (such as `Manufacturer` or `Model`).

You can see a lot about the EXIF specifications [here](http://www.exif.org/).
You can use [`exif_read_data`](http://www.php.net/manual/en/function.exif-read-data.php) to access EXIF information in php. A good code sample on how to use this command is shown in the manual within the link below.

<http://www.php.net/manual/en/function.exif-read-data.php>

But afaik currently not many cameras code the serial numbers into the EXIF blocks.