setElementImage() is used to specify a new image for the IMAGE attribute of a static form widget. The accepts two arguments - the name of a static form widget and the new value for the IMAGE attribute that is a file name with the path:
CALL fo.setElementImage ("main_label", "/images/my_image.jpg")
setElementImage()has a synonym - setFieldImage() - that is used for compatibility purpose.
When you specify a file name, be careful with its case.
UNIX is case-sensitive, so it will treat files which names come in different cases as separate files.