The splash screen is an image that appears during the startup of FreeCAD. You can disable the splash screen in the Preferences Editor by unchecking the option Enable splash screen at startup.
introduced in version 1.0: The splash screen image is picked randomly from multiple images including user models and selected add-on workbenches.
To use a custom splash screen, you have to place an image named splash_image.png in one of the following directories depending on the operating system:
The directory can be found using the App.getUserAppDataDir() command in the Python console. The Gui and images folders may have to be created first. The same custom splash screen will be used for all versions of FreeCAD on a given computer.