In a new post to her blog Vanessa Vasile shows how to use PHP to extract EXIF data from images with the help of the Exif extension.

Those of us fluent in digital photography have come across the term “Exif data” numerous times when it comes to software we use to digitally manipulate photographs. Exif (Exchangeable image file format) data is generally used to identify the properties of the camera that snapped a picture, and usually the software that altered it afterwards. [...] This quick tutorial will demonstrate how to extract Exif data from an image using PHP.

She talks about enabling the extension (if it's not already there), using it to check the image type, reading the header data and using it to great a thumbnail based on the image type.