There’s an updated Lightroom 4 version of these instructions in the Knowledgebase.
Excerpt from Adobe Lightroom 2 – The Missing FAQ
Missing files are usually a result of files being moved or renamed outside of Lightroom, perhaps in Explorer or Finder. In this case, Lightroom loses tracks of the files.
They can be identified by a little question mark in the corner of the grid thumbnail.
If the entire folder can no longer be found, the folder name in the Folders panel will go grey with a question mark folder icon. They used to go red in LR1.
When you go in to the Develop module, Lightroom will tell you that the file is offline or missing.
If the whole folder is missing and the folder name has turned grey, you can right-click on the folder and select ‘Find Missing Folder…’. Point Lightroom to the right folder, and it should update the links for all of the files contained in that folder. That’s the quickest option!
If the folder is still showing as recognised, you’ll need to relocate individual images, but Lightroom will try to help where it can.
To locate a missing file, click on the question mark icon, and the following dialog will appear.
Click Locate to find the missing file.
Locate the missing file and press Select. Check the ‘Find nearby missing photos’ checkbox shown in the dialog above in order to re-link other files in the same folder.
If you have renamed the files outside of Lightroom, each file will need linking individually.
If Lightroom appears slow to re-link related photos, restart Lightroom to force a search for ?le locations.
A few preventative measures, to avoid missing files in future:
- Rename any files before importing into Lightroom, or use Lightroom to rename them.
- Set Lightroom’s folder list to show the full folder hierarchy to a single root level folder. If all of the files are moved from their expected locations, they can easily be updated using the ‘Find Missing Folder…’ command in the top level folder right-click menu, or by using the ‘Update Folder Location…’ command even if they’re not yet marked as missing.
- Move any files or folders within Lightroom’s own interface, simply by dragging and dropping around the folders panel. Folders can only be moved one at a time.