How do I restore photos that have been removed from Lightroom, but not removed from the "disk"?
You need a backup of your Lightroom catalog file, made before the removal of the photos. Do you have such a backup? If so, find the backup catalog, open it (double-click on it) and then locate the desired photos and select them and then File->Export as Catalog; then go back to your original catalog file, open it, and select File->Import from Another Catalog and point to the catalog you just exported.
If you don't have a backup of your catalog file, then the only thing you can do is to import the photos again, and Lightroom will treat them as totally new photos with no edits and no user-supplied metadata.
By the way, the idea of importing photos into Lightroom and then later removing them from Lightroom should be limited only to photos you will NEVER want, such a photos that are so overexposed or underexposed or blurry that they are essentially useless. Photos that you care enough to perform a task on (such as editing) should never be removed from Lightroom.
Also, how do I restore photos after having backed up Lightroom.
Is this the same problem as above, or a different one?
I chose the "undo remove folders" option and it brought them back, but is saying they are all "missing or offline".
Is it possible that you actually removed the photos from the hard disk as well as from Lightroom? Anyway, Lightroom cannot find the photos and you must first find the photos on your hard disk(s) and then direct Lightroom to the photo's location on your hard disk, using these instructions Adobe Lightroom - Find moved or missing files and folders
If you have the images on your disk, then you can reimport them in Lightroom but that would not recover your edits.
The only way to get the edits back is to load your backup catalog that contain the edits.
Backup is stored at the same location as your Catalog in a backup folder.
By default, the location of backup is : Pictures\Lightroom\Backup\ and load the most recent backup catalog (with the extension .lrcat)
Refer this link : Adobe Photoshop Lightroom Help | Back up a catalog
Right click on the folder in question, and select 'Synchronize folder" and then 'Add missing photos'. This will restore the images still on the disk but removed from LR, but not the edits you made to them (if any).
Thank you. I did, unfortunately, delete them from my hard disk and had to purchase some online software to restore my hard drive. Not a good day! Backing up Lightroom is worthless if you delete them from the hard drive completely. About 75% of the pics were restored but many of those restored with very poor resolution. I was able to restore the SD cards that had the pics I needed on them. Thankfully I had moved the majority of the pics to my external hard drive a few days before. So, ultimately, I'm mostly okay with what I lost. There were only about 150 pics that I absolutely had to have that I can't recover. I'm hoping I can make due. Lesson learned! Thanks for the help!