iOSToolButton.Image
From Xojo Documentation
Property (As iOSImage )
aiOSToolButton.Image = newiOSImageValue
or
iOSImageValue = aiOSToolButton.Image
Supported on Mobile (iOS).
or
iOSImageValue = aiOSToolButton.Image
Supported on Mobile (iOS).
Specifies an image to display for the button. If you have both a Caption and Image specified, then only the Image appears.
Notes
Only the mask for the image is used, displayed using the tint color for iOS (currently blue). Also refer to these topics in the Apple iOS Human Interface Guidelines: