Technical Notes

By default, the Mac will display a giant padlock image when "Curtain Mode" is engaged with the Screens VNC app or macOS's built-in screen sharing capability:

I wanted to remove the padlock to avoid burn-in during long screen sharing sessions. I found this Apple Discussions post with the following instructions for overriding the default image:

• Create a picture using a graphics program, such as AppleWorks.
• Save the picture in PICT, TIFF, GIF, JPEG, or any other QuickTime-compatible static image format.
• QuickTime-compatible movies or QuickTime VR objects cannot be used.
  
• Name the picture "Lock Screen Picture".
  
• Copy the "Lock Screen Picture" file to /Library/Preferences/ on the client computer.

I was very dubious that it would work, but incredibly it does! If you save a plain black .tiff like this one as /Library/Preferences/Lock Screen Picture.tiff, the padlock image will disappear.