Today’s Question: Does my Lightroom catalogue contain all of my imported pictures AND associated edit recipes [adjustments], or just a link to where the pictures were imported from?
Tim’s Quick Answer: The Lightroom catalog contains a reference to your original image files on your hard drive, and also contains the metadata about your photos including adjustments you have applied in the Develop module within Lightroom.
More Detail: This is perhaps one of the most critical things to understand about Lightroom. The Lightroom catalog does not actually contain your photos, but rather manages information about your photos. You still need to keep the actual photo files on your hard drive.
When you import photos into your Lightroom catalog using the “Add” option, the photos will remain where they are, and references to those photos will be added to the catalog. Similarly, when you import photos with the “Copy” option, the source photos are copied to the destination you specify, and references to those photos are added to your catalog. In both cases you need to retain (and backup!) your actual photo files.
When you apply adjustments in the Develop module, that information is also contained in your Lightroom catalog, so that (for example) if you export an image the new file that is created in the process will reflect your adjustments.
It is worth noting that if you turn on the “Automatically write changes into XMP” checkbox on the Metadata tab of the Catalog Settings dialog, Lightroom will also write standard metadata fields and your Develop adjustment settings to an XMP sidecar file for your RAW captures or to the actual image file itself in the case of other supported image formats. This option provides a form of backup for most of the information about your photos, and improves cross-application compatibility, but is not a complete replacement for your Lightroom catalog.