Is there a way to automatically rename picture files?

When you export originals, you have three options to name the files: The original filename, the title, or a fixed name with a running number.

If you want to include the date, you first have to add the date to the title of the photo and then export the files using the "Use Title" preset.

You can use one of the scripts in the User Tip section we posted to make the renaming easier: the user Tips are here: Photos for Mac

Try for example: Script: Batch Changing the Title to the Capture Date

https://discussions.apple.com/docs/DOC-8432

Or Old Toad's modified version: Batch Change Title to Capture Date-Description-Padded Sequential Number

The Script Editor.app is utility in the folder Applications > Utilities. It is always installed with OS X.

Make a current backup of your Mac, before you try unknown scripts.

And I would test on a separate Photos Library created just for testing.

See this help page for how to switch between libraries: https://help.apple.com/photos/mac/1.0/?lang=en#/pht6d60b524

To run the script open the Script Editor application, then copy and paste the script into the window. It should look like this.

Select a few photos in your Photos Library, then press the run button.

If you should get timeout errors, select less photos.

And yes, Photos has no built-in tools to rename photos. The scripts are all we have in Photos.

You could try tools like "A Better Finder" to help with renaming files.

There is no way to automatically rename exported photos to a custom string using Photos

You can using other software after export - look in the App store or use a web search to see if you can find something that will do you specific job

and you can use Photos to set the name to the photos title - it is possible that you could write (or have written) a custom to set the title to the desired file and and then use the Photos capability to set the exported file name to the title

LN