I've been scanning in a bunch of old photos. A number of them have notes written on the back. While I've added metadata to the scans (dates, names, places), I've also scanned the backs because I'd like to retain those original handwritten notes. Is there any way to link the two images (front and back of the one photo) together? (aside from making one double-width image with front and back side by side)
If you don't want to join the two sides into a double wide image you can give the two images the same name but one with "-F' (for front) and the other with "-B" (for back) or -1 and -2.
This can be done outside of the Photos library with a renaming app like Name Mangler.
It could also be done within the Photos Library with this AppleScript: Batch Change Title to Text w/Padded Sequential Numbers.
The script compiled as an application can be downloaded from this tutorial site: P01 - Applescripts from Photos’ User Tips Compiled as Applications
If you do want both the front and back in the same image you'll need an image editor that can handle layers like GraphicConverter. You can try the demo version before purchasing.
Another option would be to use the title field. - EG Pair00 Pair01 etc. Giving both photos of a pair the same number.
Linking photos together
