iOSToolButton.Image

From Xojo Documentation

Property (As iOSImage )
aiOSToolButton.Image = newiOSImageValue
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: