Get/set the description of the corresponding media item in the Photos app.

In the macOS Photos app, you can set a “caption” for a photo (select Window > Info, then look for the Caption field below a photo).

As far as I can tell, the only way to manage this caption programatically is using AppleScript – it’s not exposed to the PhotoKit APIs.

Get the description

Look at the description field of a media item from the Photos Suite. Here’s a script that takes a local identifier as an argument, and prints the caption (if set):

#!/usr/bin/env osascript

on run argv
  set targetId to item 1 of argv

  tell application "Photos"
    set targetMedia to media item id targetId
    set desc to description of targetMedia
    
    if desc is missing value then
      return ""
    else
      return desc
    end if
  end tell
end run

Set the description

Set the description field. Here’s a script that takes a local identifier and new caption as arguments:

#!/usr/bin/env osascript

on run argv
  set targetId to item 1 of argv
  set newCaption to item 2 of argv

  tell application "Photos"
    set targetMedia to media item id targetId
    set description of targetMedia to newCaption
  end tell
end run