Don't forget that x+xw is one pixel more than the actual width of a rect/image. So for totally accurate checking:
If MouseX()>=x And MouseX()<x+w and MouseY()>=y and MouseY()<y+yw
Or, in shorthand:
If RectsOverlap( MouseX(), MouseY(), 1, 1, x, y, xw, yw )
Or:
If ImageRectOverlap( off_image, x, y, MouseX(), MouseY(), 1, 1 )
If MouseX()>=x And MouseX()<x+w and MouseY()>=y and MouseY()<y+yw
Or, in shorthand:
If RectsOverlap( MouseX(), MouseY(), 1, 1, x, y, xw, yw )
Or:
If ImageRectOverlap( off_image, x, y, MouseX(), MouseY(), 1, 1 )