You can use many of the small (meaning 1.5“ or 1.8”) LCD keychain picture frames under Linux.
You need gphoto2 to send photos to the picture frame and you need libgphoto2-2 for the drivers.
Below are a few commands to get pics on the frame.
List all pictures
gphoto2 -L
Delete all pictures
gphoto2 -D
Add a picture
ghoto2 <filename>