In LR, "Photo Booth" is called a keyword (or keyword tag). Two possibilities:
1. "Photo Booth" exists in the photos' metadata prior to importing into LR. It could be stored in the fields IPTC:Keywords, XMP:Subject, or XMP:HierarchicalSubject. The free ExifTool utilty is the most authoritative tool for examining file metadata. This command line will show you all the fields in a file:
exiftool -a -G filename
2. You have a metadata preset being applied during Import that assigns the keyword to the imported photos. To troubleshoot this, do an import of fresh photos never-before-imported into LR, setting Apply During Import > Metadata to None:
Thanks for the advice. I've had a trawl around the data and discovered that "Photo Booth" was a tag in IPTC keywords. Not sure where it came from but most likely something I used about 5 years ago and thought I had got rid of. Thanks again.
Glad you identified the problem.