The image form element does not have a value attribute.
when an image for element type is used, no value will be passed, but it will pass the x and y coordinates of where the mouse clicked the image.
you can demonstrate this by creating a simple for with an image field and setting the method to get, you will see in the querystring:
since you cant check for the image fields value, you need to check for the x or y coordinates:
PowerStore was not coded to use an image field, it was coded to use a standard submit button.
if you swap a standard submit button with an image field, you will break the trigger code for the element.