The Zend Developer Zone has a new tutorial from Vikram Vaswani looking at the reading and writing of metadata for mp3s and images with two handy PECL extensions.
It's just that every time I sit down to have a go at [finding something in my photo or mp3 library], the sheer volume of data overwhelms me and I take the command decision to deal with something easier instead. Sounds familiar? If it does, help is at hand, in the form of PHP's ID3 and EXIF extensions. These extensions can help you organize and catalog your digital media collection so that it's easier to navigate and search. Keep reading, and I'll show you how.
He installs the ID3 package first (via the pecl command line tool) and gives a few sample scripts to pull the metadata information out of a mp3 file as well as update/remove the information that's already there. He even sets up a simple SQLite database to store the information he's retrieved.
The second part of the tutorial looks at grabbing the image metadata via the EXIF extension. This can yield all sorts of information including date/time the photo was taken, the resolution, the model of the camera and various camera settings at the time. He includes a sample script that automatically makes thumbnails for the images via the exif_thumbnail function.