Is there any way to recover these? I can't downgrade the version. and it's hosed in v24.
With 20-30 pictures, at your place, I would try to avoid a migration and prefer clean file upload.
Use a backup of the database, install a Tiki 21 and download the few pictures you have. Open the Tiki 24 and upload them in files galleries.
But... may be you don't have a backup of the database? (you should have somewhere and may be you don't know)
If so I'm not sure if the tables are somewhere in your database.
Look to me that this require a deeper check. Feel free to contact me in private or any Tiki consultants available and able to help.
I would also create a ticket at dev.tiki.org and explain the issue and situation. (no auto-migration and no warning, no way to do a migration once on Tiki 24, what you experienced, etc)