How to Customize the Crop Guide Overlay
The crop guide or cropping mask you see in FLOW can be customized. FLOW references a transparent PNG file called crop_overlay.png in the Overlays folder (C:\ProgramData\Flow\Overlays). You can customize this file in an editing software and save it back into the Overlays folder.
Navigate to C:\ProgramData\Flow\Overlays and locate crop_overlay.png.
Edit the file in PhotoShop or editing software
Save your graphic as a new transparent PNG back to the same location and relaunch FLOW
Set the default Crop Guide for FLOW in Preferences -> Capture -> Display tab
Uncheck default overlay PNG and navigate to the prefered overlay to use for each orientation