Keep the original name for photos - for scanned images give each image a permanent "ID number".
I assume you would like to be able to view the photos in chronological order - that part can be added to the file name then or later.
The final file name would then be in this form "Year_DateSequenceNumber_IDxxxx. jpg":
1950_021_ID1026. jpg etc. etc.
FWIW when I scanned my photos I used the first part (1950-020. jpg) as the "file ID" and later found some photos were in the wrong year. I can't change that easily and I can't put them in sequence. . . Using an independent ID (tracking number) allows you change the year and the date sequence.
You might want to add names and/or occasions at the end (the KISS approach).
You may want to do more. . . I use a spreadsheet with info about each photo (who, where, occasion, notes/comments) and am now creating individual HTML files for each photo - then grouping them on PHP web pages for viewing - using EasyPHP.