I use a Mac Pro as my favored control for edits and such. Most of the time, the drag n drop feature for new artist pics does not function reliably. I vaguely recall a time when I could drag n drop pics, and there is every indication it should work, but it hasn’t worked for me in quite a while.
If this feature won’t always work, I’d recommend removing it. But I’d rather you fixed it.
PS: if your code is some well-meaning copyright protection effort, that’s okay, but tell the user that’s why it isn’t working. Also, know that such code is easily defeated.
Would it be possible for you to reproduce this behavior while recording a screen capture? macOS Mojave introduced a new built-in screen capture tool that makes this pretty easy to do, you can read more about how to use it here.
Once you have recorded the screen capture, upload it using a file sharing service like Firefox Send and share it with us here.