Image metadata is plain text information embedded into the image file.
This can include details relevant to the image like shooting information (F-stop) as well as information about its location, subject, keywords, and copyright - to name a few of the more common ones.
The image gallery has extensive support for all the metadata you need.
There are three types of metadata commonly found in images; IPTC, EXIF, and XMP
EXIF is read only - mostly camera info, though other user data like the person who took the image may be stored there (in EXIF Creator tag) if the photographer sets their camera up right. The toolkit always copies this field to IPTCCreator field, which can be seen easily in Windows Explorer. If you then set up your columns in pane view and you will be able to manually filter whole directories by one creator. What's so good about that? It's 2 AM and a client is screaming, but the db is down for maintenance so you have to find an image manually... You get my drift.
IPTC: this is the metdata standard created by the global standards body of the news media. This is meant to be written to so journalists can transfer information with the files they send their editors. It has wide support for reading. In Adobe Bridge (the photographers #1 image file asset manager) you can search and filter whole directories on the IPTC keywords field. It is not practical in a webserver environment to search metadata like this, that is why your need a database.
XMP is a relatively new standard and therefore could soon be forgotten (like Silverlight). Coders might feel at home because it is XML based but Adobe’s Extensible Metadata Platform is a bit proprietary for me. I want my metadata to be visible in not just Adobe Bridge but in Windows Explorer too.
For metadata to be useful you need to know what maps to what e.g. IPTCKeywords maps to WinEx Tags, Bridge Keywords, IptcByline maps to Windows Explorer: Authors and Adobe Bridge: Creator and Exif: Artist. I've don all that so you don't have to - my toolkit has extensive support for all the metadata you need.
Note: not all image formats support metadata - jpeg does!
Want to know more about metadata <https://www.google.com/search?q=image+metadata>