Metadata is image information stored alongside or within a photo. You don’t see it in the image, but it can be read by different software applications to help filter, sort, search or identify images.
Metadata comes in a number of different types, including camera EXIF data, IPTC metadata, catalog metadata and image adjustment metadata. Here’s a look at all four, what they’re used for and some of the jargon around them.
EXIF data is basic camera and shooting information stored by cameras within every image you capture. This metadata will typically include the brand and model of the camera, the brand and model of the lens (if different), the shutter speed, lens aperture setting and ISO setting.
The EXIF data will also include the time and date the picture was taken, and this can be particularly important later when you want to sort out your pictures chronologically. For this reason alone it’s important to set the time and date correctly on your camera.
If you’re taking pictures with a phone, the EXIF data will also include location information. If you shoot with a regular camera, this won’t be included unless the camera is GPS-enabled or you’ve got it connected wirelessly to your smartphone to synchronise location data.
Where EXIF data is embedded automatically by your camera and cannot be changed, IPTC data is optional information you can add in image browsing or cataloguing software and which is used by press agencies and image libraries. It includes a standardised set of fields such as Description, Keywords, Copyright and more. You don’t have to fill them all in – in fact you don’t have to fill any of them in – though some of this information can be useful.
Keywords are used widely in image cataloguing software to help with searching and filtering images. You can add as many keywords as you like to an image, and search for images based on a single keyword or several.
Filling in copyright information is a wise precaution if you are sharing your images for publication. Adding copyright information doesn’t prevent anyone from stealing your image if they want to, but if a bona fide publisher comes across your image and wants to use it, the copyright information will tell them that it’s owned and not free to use, and the name of the photographer they need to contact for permission.
IPTC metadata can also include star ratings for images. Some cameras let you add star ratings in-camera, while most image browsing and cataloguing programs let you add star ratings too.
Image cataloguing software may not automatically embed any new data you add into the original image files. Most programs take the approach that they will not modify original files in any way unless you specifically request it.
Cataloguing software may store new image data you add in the catalog file itself, or as ‘sidecar’ files alongside the original images. This also applies to image adjustment metadata used by non-destructive photo editors like Lightroom.
Non-destructive editing means your original images are never modified – so if your adjustments aren’t stored in the image itself, they have to be stored somewhere. Lightroom and Capture One typically store adjustments in their catalog files, so that if the connection between the database record and the ‘referenced’ image is lost, so are the adjustments made to that image.
Non-destructive editors may also store adjustments as ‘sidecar’ files. Adobe Bridge will do this with adjustments made in Camera Raw, saving xmp files alongside photos (the xmp format is Adobe’s favored metadata format). ON1 Photo RAW will save its own sidecar adjustment files alongside photos, while Capture One (in Sessions mode) and Exposure X save adjustment metadata in separate subfolders.
The point is that if you see lots of small data files appearing alongside your photos, these are adjustment metadata left by non-destructive editors. If you delete these metadata files, or move the images but not these files, your adjustments will become separated and lost.